April 2008 - Darwin-dev - lists.apple.com

Re: mach_absolute_time() vs. sleep() [solved]
by Kristopher Matthews 30 Apr '08

30 Apr '08

site_archiver(a)lists.apple.com Delivered-To: Darwin-dev(a)lists.apple.com -(double)machElapsedTime:(uint64_t) start endTime: (uint64_t) endTime { uint64_t diff = endTime - start; static double conversion = 0.0; if (conversion == 0.0) { mach_timebase_info_data_t info; kern_return_t err = mach_timebase_info(&info); if (err == 0) conversion = info.denom / 1e9 * info.numer; } return diff * conversion; } On Apr 30, 2008, at 5:52 PM, Kristopher Matthews wrote: It was my fault. It turned out to be a pretty idiotic problem: should be "return diff / conversion;" Go go copying samples. For completeness: -(double)machElapsedTime:(uint64_t) start endTime: (uint64_t) endTime { uint64_t diff = endTime - start; static double conversion = 0.0; if (conversion == 0.0) { mach_timebase_info_data_t info; kern_return_t err = mach_timebase_info(&info); if (err == 0) conversion = 1e9 * info.numer / info.denom; } return diff / conversion; } On Apr 30, 2008, at 4:09 PM, Terry Lambert wrote: Can you assure me that this is not for a homework assignment? -- Terry On Apr 30, 2008, at 3:30 PM, Terry Lambert wrote: It should be: double mach_elapsed_time(uint64_t start, uint64_t endTime) { _______________________________________________ Do not post admin requests to the list. They will be ignored. Darwin-dev mailing list (Darwin-dev(a)lists.apple.com) Help/Unsubscribe/Update your Subscription: http://lists.apple.com/mailman/options/darwin-dev/kmmx%40mac.com _______________________________________________ Do not post admin requests to the list. They will be ignored. Darwin-dev mailing list (Darwin-dev(a)lists.apple.com) Help/Unsubscribe/Update your Subscription: http://lists.apple.com/mailman/options/darwin-dev/site_archiver%40lists.app… This email sent to site_archiver(a)lists.apple.com As "Ahruman" on freenode pointed out, it's faster to swap the original divide and use a multiply at the end: (PS. That code is actually from http://macresearch.org/tutorial_performance_and_time ) return conversion * (double) diff; Actually, it doesn't; the margin is just small enough that you don't notice it. On Apr 30, 2008, at 1:34 PM, Kristopher Matthews wrote: Care to elaborate? This code works fine in all circumstances where sleep() is not called. On Apr 30, 2008, at 4:13 AM, Kristopher Matthews wrote: If you see my followup message, I wrote the sample code for this email incorrectly. My apologies. :) You are doing a couple of really simple things wrong, but the worst is being wrong about operator precedence order in C. This email sent to kmmx(a)mac.com smime.p7s

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Re: mach_absolute_time() vs. sleep() [solved]
by Kristopher Matthews 30 Apr '08

30 Apr '08

site_archiver(a)lists.apple.com Delivered-To: Darwin-dev(a)lists.apple.com It was my fault. It turned out to be a pretty idiotic problem: should be "return diff / conversion;" Go go copying samples. For completeness: -(double)machElapsedTime:(uint64_t) start endTime: (uint64_t) endTime { uint64_t diff = endTime - start; static double conversion = 0.0; if (conversion == 0.0) { mach_timebase_info_data_t info; kern_return_t err = mach_timebase_info(&info); if (err == 0) conversion = 1e9 * info.numer / info.denom; } return diff / conversion; } On Apr 30, 2008, at 4:09 PM, Terry Lambert wrote: Can you assure me that this is not for a homework assignment? -- Terry On Apr 30, 2008, at 3:30 PM, Terry Lambert wrote: It should be: double mach_elapsed_time(uint64_t start, uint64_t endTime) { _______________________________________________ Do not post admin requests to the list. They will be ignored. Darwin-dev mailing list (Darwin-dev(a)lists.apple.com) Help/Unsubscribe/Update your Subscription: http://lists.apple.com/mailman/options/darwin-dev/site_archiver%40lists.app… This email sent to site_archiver(a)lists.apple.com return conversion * (double) diff; Actually, it doesn't; the margin is just small enough that you don't notice it. On Apr 30, 2008, at 1:34 PM, Kristopher Matthews wrote: Care to elaborate? This code works fine in all circumstances where sleep() is not called. On Apr 30, 2008, at 4:13 AM, Kristopher Matthews wrote: If you see my followup message, I wrote the sample code for this email incorrectly. My apologies. :) You are doing a couple of really simple things wrong, but the worst is being wrong about operator precedence order in C. smime.p7s

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Re: mach_absolute_time() vs. sleep()
by Terry Lambert 30 Apr '08

30 Apr '08

site_archiver(a)lists.apple.com Delivered-To: Darwin-dev(a)lists.apple.com Can you assure me that this is not for a homework assignment? -- Terry On Apr 30, 2008, at 3:30 PM, Terry Lambert wrote: It should be: double mach_elapsed_time(uint64_t start, uint64_t endTime) { _______________________________________________ Do not post admin requests to the list. They will be ignored. Darwin-dev mailing list (Darwin-dev(a)lists.apple.com) Help/Unsubscribe/Update your Subscription: http://lists.apple.com/mailman/options/darwin-dev/site_archiver%40lists.app… Actually, it doesn't; the margin is just small enough that you don't notice it. On Apr 30, 2008, at 1:34 PM, Kristopher Matthews wrote: Care to elaborate? This code works fine in all circumstances where sleep() is not called. On Apr 30, 2008, at 4:13 AM, Kristopher Matthews wrote: If you see my followup message, I wrote the sample code for this email incorrectly. My apologies. :) You are doing a couple of really simple things wrong, but the worst is being wrong about operator precedence order in C. This email sent to site_archiver(a)lists.apple.com

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Re: mach_absolute_time() vs. sleep()
by Kristopher Matthews 30 Apr '08

30 Apr '08

site_archiver(a)lists.apple.com Delivered-To: Darwin-dev(a)lists.apple.com On Apr 30, 2008, at 3:30 PM, Terry Lambert wrote: It should be: double mach_elapsed_time(uint64_t start, uint64_t endTime) { _______________________________________________ Do not post admin requests to the list. They will be ignored. Darwin-dev mailing list (Darwin-dev(a)lists.apple.com) Help/Unsubscribe/Update your Subscription: http://lists.apple.com/mailman/options/darwin-dev/site_archiver%40lists.app… This email sent to site_archiver(a)lists.apple.com Care to elaborate? This code works fine in all circumstances where sleep() is not called. On Apr 30, 2008, at 4:13 AM, Kristopher Matthews wrote: If you see my followup message, I wrote the sample code for this email incorrectly. My apologies. :) You are doing a couple of really simple things wrong, but the worst is being wrong about operator precedence order in C. -- Terry smime.p7s

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Re: mach_absolute_time() vs. sleep()
by Terry Lambert 30 Apr '08

30 Apr '08

site_archiver(a)lists.apple.com Delivered-To: Darwin-dev(a)lists.apple.com It should be: double mach_elapsed_time(uint64_t start, uint64_t endTime) { -- Terry _______________________________________________ Do not post admin requests to the list. They will be ignored. Darwin-dev mailing list (Darwin-dev(a)lists.apple.com) Help/Unsubscribe/Update your Subscription: http://lists.apple.com/mailman/options/darwin-dev/site_archiver%40lists.app… On Apr 30, 2008, at 4:13 AM, Kristopher Matthews wrote: If you see my followup message, I wrote the sample code for this email incorrectly. My apologies. :) You are doing a couple of really simple things wrong, but the worst is being wrong about operator precedence order in C. This email sent to site_archiver(a)lists.apple.com

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Virtual COM driver issue - dlil_ouput output error retval =37
by Ashish Kumar Kalvakota 30 Apr '08

30 Apr '08

site_archiver(a)lists.apple.com Delivered-To: darwin-dev(a)lists.apple.com Organization: Tata Elxsi Ltd Thread-index: AciqyYUcJbxm2jyDTwmztSxAPh+zGA== _______________________________________________ Do not post admin requests to the list. They will be ignored. Darwin-dev mailing list (Darwin-dev(a)lists.apple.com) Help/Unsubscribe/Update your Subscription: http://lists.apple.com/mailman/options/darwin-dev/site_archiver%40lists.app… This email sent to site_archiver(a)lists.apple.com

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Re: userland supported APIs (was: Re: Synchronization primitives)
by Army Research Lab 30 Apr '08

30 Apr '08

site_archiver(a)lists.apple.com Delivered-To: darwin-dev(a)lists.apple.com Thread-index: AciqtAjjR7GDeRanEd2+zgAdT0T19A== Thread-topic: userland supported APIs (was: Re: Synchronization primitives) User-agent: Microsoft-Entourage/11.4.0.080122 On 4/29/08 3:14 PM, "Terry Lambert" <tlambert(a)apple.com> wrote: <<SNIP>> >> 3) There isn't anything quite like the OSAtomic* operators in user >> space >> that are truly supported (that is, won't be removed in the future >> during >> cleanup), and therefore if I want shared variables, I need to use >> pthread_mutex_lock(), write my variable, and then unlock(). > > If it's currently documented, it's currently supported. Shawn already > pointed you at the documentation. > > We don't really guarantee anything about future support, and I and the > rest of us (Dave Z., Shawn, etc.) are prohibited by our employment > contracts from making those kinds of statements. They are above our > pay grade. > > If you need that kind of official statement, you need to file a bug to > get it (or an official "no comment"). > > Being from a military lab, you are undoubtedly familiar with "chain of > command". You are currently talking to S4s in a mess tent. 8-). :D Trust me, I understand completely! As it stands, I think I will use them, but I'll wrap them carefully. I don't know if you're allowed to give an opinion on this or not, but I'll ask anyways (and this is for all the Apple guys that are willing to comment): do you guys at least like the signatures/functionality of the functions in /usr/include/libkern? That is, if the functions were moved/renamed would they still behave in exactly the same manner, if you had a choice in the matter? If you don't think you can answer, I understand. Thanks, Cem Karan _______________________________________________ Do not post admin requests to the list. They will be ignored. Darwin-dev mailing list (Darwin-dev(a)lists.apple.com) Help/Unsubscribe/Update your Subscription: http://lists.apple.com/mailman/options/darwin-dev/site_archiver%40lists.app… This email sent to site_archiver(a)lists.apple.com

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Re: mach_absolute_time() vs. sleep()
by Kristopher Matthews 30 Apr '08

30 Apr '08

site_archiver(a)lists.apple.com Delivered-To: Darwin-dev(a)lists.apple.com It should be: double mach_elapsed_time(uint64_t start, uint64_t endTime) { Thanks. :) On Apr 29, 2008, at 10:29 PM, Terry Lambert wrote: double mach_elapsed_time(double start, double endTime) { uint64_t diff = endTime - start; static double conversion = 0.0; if (conversion == 0.0) { mach_timebase_info_data_t info; kern_return_t err = mach_timebase_info(&info); if (err == 0) conversion = 1e-9 * (double) info.numer / (double) info.denom; } return conversion * (double) diff; } uint64_t s = mach_absolute_time(); NSLog(@"test"); double duration = mach_elapsed_time(s, mach_absolute_time()); uint64_t s = mach_absolute_time(); sleep(6); double duration = mach_elapsed_time(s, mach_absolute_time()); _______________________________________________ Do not post admin requests to the list. They will be ignored. Darwin-dev mailing list (Darwin-dev(a)lists.apple.com) Help/Unsubscribe/Update your Subscription: http://lists.apple.com/mailman/options/darwin-dev/site_archiver%40lists.app… This email sent to site_archiver(a)lists.apple.com If you see my followup message, I wrote the sample code for this email incorrectly. My apologies. :) On Apr 29, 2008, at 6:01 PM, Kristopher Matthews wrote: I'm having some strange trouble with these two calls. Example code follows. At this point, "duration" is a reasonable value in seconds. (About 0.005 IIRC.) This code also works for measuring another block of code I have that write several mbs to disk - the time it reports is in line with the difference between NSLog statements. But this: Produces completely unrealistic results - this specific example comes in at 0.387 seconds. Any thoughts? (I know, I know. this is a BS test case. I just happened upon it and I'm curious why this happens. I have no other problem with timing in this manner.) The type double and uint64_t are not the same type. A uint64_t is a 64 bit integer. Why are you dragging floating point into this without an explicit cast of the function arguments to doubles, and then expecting this to work? -- Terry smime.p7s

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Re: mach_absolute_time() vs. sleep()
by Terry Lambert 30 Apr '08

30 Apr '08

site_archiver(a)lists.apple.com Delivered-To: Darwin-dev(a)lists.apple.com double mach_elapsed_time(double start, double endTime) { uint64_t diff = endTime - start; static double conversion = 0.0; if (conversion == 0.0) { mach_timebase_info_data_t info; kern_return_t err = mach_timebase_info(&info); if (err == 0) conversion = 1e-9 * (double) info.numer / (double) info.denom; } return conversion * (double) diff; } uint64_t s = mach_absolute_time(); NSLog(@"test"); double duration = mach_elapsed_time(s, mach_absolute_time()); uint64_t s = mach_absolute_time(); sleep(6); double duration = mach_elapsed_time(s, mach_absolute_time()); -- Terry _______________________________________________ Do not post admin requests to the list. They will be ignored. Darwin-dev mailing list (Darwin-dev(a)lists.apple.com) Help/Unsubscribe/Update your Subscription: http://lists.apple.com/mailman/options/darwin-dev/site_archiver%40lists.app… On Apr 29, 2008, at 6:01 PM, Kristopher Matthews wrote: I'm having some strange trouble with these two calls. Example code follows. At this point, "duration" is a reasonable value in seconds. (About 0.005 IIRC.) This code also works for measuring another block of code I have that write several mbs to disk - the time it reports is in line with the difference between NSLog statements. But this: Produces completely unrealistic results - this specific example comes in at 0.387 seconds. Any thoughts? (I know, I know. this is a BS test case. I just happened upon it and I'm curious why this happens. I have no other problem with timing in this manner.) The type double and uint64_t are not the same type. A uint64_t is a 64 bit integer. Why are you dragging floating point into this without an explicit cast of the function arguments to doubles, and then expecting this to work? This email sent to site_archiver(a)lists.apple.com

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Re: mach_absolute_time() vs. sleep()
by Kristopher Matthews 30 Apr '08

30 Apr '08

site_archiver(a)lists.apple.com Delivered-To: Darwin-dev(a)lists.apple.com uint64_t s = mach_absolute_time(); sleep(6); double duration = mach_elapsed_time(s, mach_absolute_time()); Thanks, Kris On Apr 29, 2008, at 8:10 PM, Alison Cassidy wrote: Hi there, -- Allie On Apr 29, 2008, at 6:01 PM, Kristopher Matthews wrote: double mach_elapsed_time(double start, double endTime) { uint64_t diff = endTime - start; static double conversion = 0.0; if (conversion == 0.0) { mach_timebase_info_data_t info; kern_return_t err = mach_timebase_info(&info); if (err == 0) conversion = 1e-9 * (double) info.numer / (double) info.denom; } return conversion * (double) diff; } uint64_t s = mach_absolute_time(); NSLog(@"test"); double duration = mach_elapsed_time(s, mach_absolute_time()); uint64_t s = mach_absolute_time(); sleep(6); double duration = mach_elapsed_time(s, mach_absolute_time()); Regards, Kris _______________________________________________ Do not post admin requests to the list. They will be ignored. Darwin-dev mailing list (Darwin-dev(a)lists.apple.com) Help/Unsubscribe/Update your Subscription: http://lists.apple.com/mailman/options/darwin-dev/cooties%40mac.com _______________________________________________ Do not post admin requests to the list. They will be ignored. Darwin-dev mailing list (Darwin-dev(a)lists.apple.com) Help/Unsubscribe/Update your Subscription: http://lists.apple.com/mailman/options/darwin-dev/site_archiver%40lists.app… This email sent to site_archiver(a)lists.apple.com Yeah. My curiosity is that by NSLog output, it is sleeping approximately the time I specify - so This does take about sex seconds (and I can see that from the NSLog output as well, having a statement before and after). My issue is that 'duration' here is far less than six seconds - less than half a second, even though the code definitely took six seconds to execute. Perhaps there is some other subtle error with my code. I'll keep digging. I've had exactly this experience in the past, too while working on a streaming server. The sleep() command regularly gets interrupted early and cannot be relied upon for accurate delays. I used mach_absolute_time() and mach_wait_until() with some calculations to convert ticks into microseconds to get accurate delays (without thread suspension). The man pages give a hint as to why it may be happening; "The sleep() function suspends execution of the calling thread until either seconds seconds have elapsed or a signal is delivered to the thread [...] If the sleep() function returns because the requested time has elapsed, the value returned will be zero. If the sleep() function returns due to the delivery of a signal, the value returned will be the unslept amount (the requested time minus the time actually slept) in seconds." I'm having some strange trouble with these two calls. Example code follows. At this point, "duration" is a reasonable value in seconds. (About 0.005 IIRC.) This code also works for measuring another block of code I have that write several mbs to disk - the time it reports is in line with the difference between NSLog statements. But this: Produces completely unrealistic results - this specific example comes in at 0.387 seconds. Any thoughts? (I know, I know. this is a BS test case. I just happened upon it and I'm curious why this happens. I have no other problem with timing in this manner.) This email sent to cooties(a)mac.com smime.p7s

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