Re: IOFIES Filter wakeup (was: why no IOSimpleLockSleep()?)

Subject: Re: IOFIES Filter wakeup (was: why no IOSimpleLockSleep()?)

From: Chris Sarcone <email@hidden>

Date: Thu, 26 May 2005 12:39:16 -0700

Delivered-to: email@hidden

Drew --

When using a filter interrupt with Tiger, I see a roughly 20% latency
reduction (10us -> 8us) and with Panther, I see a nearly 40% reduction
(17.1us -> 9.9us). This is atop a hardware overhead of roughly 3.5us,
which is constant regardless of platform.

It is interesting to note that Tiger is *MUCH* faster at either
scheduling interrupt threads, or at scheduling threads in general than
Panther is. Kudos to whomever was responsible for this improvement.

Yes it is quite a bit faster! Kernel engineers modified the scheduler bits to be much faster, added primitives to make IOWorkLoop threads faster (thread_block_parameter() instead of thread_get_cont_arg()/thread_set_cont_arg()) and also modified the IOSharedInterruptController code to have better performance (all of which directly impacted those latency measurements).

Our IOPS numbers increased quite a bit on FibreChannel disk arrays due to the above changes, the removal of the kernel funnels, and some other optimizations on the I/O path (including removing some DART setup cost, not allocating sense data descriptors on transports that provide auto-sense data, etc.).

-- Chris

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References:
	>why no IOSimpleLockSleep()? (From: Andrew Gallatin <email@hidden>)
	>IOFIES Filter wakeup (was: why no IOSimpleLockSleep()?) (From: Godfrey van der Linden <email@hidden>)
	>Re: IOFIES Filter wakeup (was: why no IOSimpleLockSleep()?) (From: Andrew Gallatin <email@hidden>)
	>Re: IOFIES Filter wakeup (was: why no IOSimpleLockSleep()?) (From: Godfrey van der Linden <email@hidden>)
	>Re: IOFIES Filter wakeup (was: why no IOSimpleLockSleep()?) (From: Andrew Gallatin <email@hidden>)
	>Re: IOFIES Filter wakeup (was: why no IOSimpleLockSleep()?) (From: Andrew Gallatin <email@hidden>)