From: "H. Peter Anvin" <hpa@zytor.com>
To: Mike Galbraith <bitbucket@online.de>
Cc: Andi Kleen <andi@firstfloor.org>,
linux-kernel@vger.kernel.org, x86@kernel.org, mingo@kernel.org,
torvalds@linux-foundation.org
Subject: Re: Re-tune x86 uaccess code for PREEMPT_VOLUNTARY
Date: Sat, 10 Aug 2013 21:57:26 -0700 [thread overview]
Message-ID: <f6227e5d-597b-4818-876a-3a21893cdd93@email.android.com> (raw)
In-Reply-To: <1376195819.7006.18.camel@marge.simpson.net>
That sounds like an issue with specific preemption policies.
Mike Galbraith <bitbucket@online.de> wrote:
>On Sat, 2013-08-10 at 21:27 -0700, H. Peter Anvin wrote:
>> On 08/10/2013 09:17 PM, Mike Galbraith wrote:
>> >>
>> >> Do you have any quantification of "munches throughput?" It seems
>odd
>> >> that it would be worse than polling for preempt all over the
>kernel, but
>> >> perhaps the additional locking is what costs.
>> >
>> > I hadn't compared in ages, so made some fresh samples.
>> >
>> > Q6600 3.11-rc4
>> >
>> > vmark
>> > voluntary 169808 155826 154741 1.000
>> > preempt 149354 124016 128436 .836
>> >
>> > That should be ~worst case, it hates preemption.
>> >
>> > tbench 8
>> > voluntary 1027.96 1028.76 1044.60 1.000
>> > preempt 929.06 935.01 928.64 .900
>> >
>> > hackbench -l 10000
>> > voluntary 23.146 23.124 23.230 1.000
>> > preempt 25.065 24.633 24.789 1.071
>> >
>> > kbuild vmlinux
>> > voluntary 3m44.842s 3m42.975s 3m42.954s 1.000
>> > preempt 3m46.141s 3m45.835s 3m45.953s 1.010
>> >
>> > Compute load comparisons are boring 'course.
>> >
>>
>> I presume voluntary is indistinguishable from no preemption at all?
>
>No, all preemption options produce performance deltas.
>
>> Either way, that is definitely a reproducible test case, so if
>someone
>> is willing to take on optimizing preemption they can use vmark as the
>> litmus test. It would be really awesome if we genuinely could get
>the
>> cost of preemption down to where it just doesn't matter.
>
>You have to eat more scheduler cycles, that's what PREEMPT does for a
>living. Release a lock, wham.
>
>-Mike
--
Sent from my mobile phone. Please excuse brevity and lack of formatting.
next prev parent reply other threads:[~2013-08-11 4:57 UTC|newest]
Thread overview: 40+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-08-09 23:04 Andi Kleen
2013-08-09 23:04 ` [PATCH 01/13] x86: Add 1/2/4/8 byte optimization to 64bit __copy_{from,to}_user_inatomic Andi Kleen
2013-08-09 23:04 ` [PATCH 02/13] x86: Include linux/sched.h in asm/uaccess.h Andi Kleen
2013-08-09 23:04 ` [PATCH 03/13] tree-sweep: Include linux/sched.h for might_sleep users Andi Kleen
2013-08-09 23:04 ` [PATCH 04/13] Move might_sleep and friends from kernel.h to sched.h Andi Kleen
2013-08-09 23:04 ` [PATCH 05/13] sched: mark should_resched() __always_inline Andi Kleen
2013-08-09 23:04 ` [PATCH 06/13] x86: Add 32bit versions of SAVE_ALL/RESTORE_ALL to calling.h Andi Kleen
2013-08-09 23:04 ` [PATCH 07/13] Add might_fault_debug_only() Andi Kleen
2013-08-14 18:24 ` Michael S. Tsirkin
2013-08-09 23:04 ` [PATCH 08/13] x86: Move cond_resched into the out of line put_user code Andi Kleen
2013-08-09 23:04 ` [PATCH 09/13] x86: Move cond_resched into the out of line get_user code Andi Kleen
2013-08-09 23:04 ` [PATCH 10/13] x86: Move cond resched for copy_{from,to}_user into low level code 64bit Andi Kleen
2013-08-10 15:42 ` Linus Torvalds
2013-08-10 16:10 ` Andi Kleen
2013-08-10 16:27 ` Linus Torvalds
2013-08-10 18:23 ` Borislav Petkov
2013-08-10 19:05 ` Jörn Engel
2013-08-20 21:03 ` KOSAKI Motohiro
2013-08-15 5:04 ` Michael S. Tsirkin
2013-08-09 23:04 ` [PATCH 11/13] sched: Inline the need_resched test into the caller for _cond_resched Andi Kleen
2013-08-09 23:04 ` [PATCH 12/13] x86: move __copy_*_nocache might fault check out of line Andi Kleen
2013-08-09 23:04 ` [PATCH 13/13] x86: drop cond rescheds from __copy_{from,to}_user Andi Kleen
2013-08-10 4:42 ` Re-tune x86 uaccess code for PREEMPT_VOLUNTARY H. Peter Anvin
2013-08-10 5:55 ` Mike Galbraith
2013-08-10 16:09 ` H. Peter Anvin
2013-08-10 16:43 ` Linus Torvalds
2013-08-10 17:18 ` H. Peter Anvin
2013-08-10 18:51 ` Linus Torvalds
2013-08-10 19:18 ` H. Peter Anvin
2013-08-10 20:26 ` H. Peter Anvin
2013-08-10 23:00 ` H. Peter Anvin
2013-08-11 4:17 ` Mike Galbraith
2013-08-11 4:27 ` H. Peter Anvin
2013-08-11 4:36 ` Mike Galbraith
2013-08-11 4:57 ` H. Peter Anvin [this message]
2013-08-11 5:58 ` Mike Galbraith
2013-08-13 18:09 ` H. Peter Anvin
2013-08-13 18:12 ` Andi Kleen
2013-08-14 18:27 ` Michael S. Tsirkin
2013-08-14 22:08 ` Andi Kleen
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