From: Ingo Molnar <mingo@kernel.org>
To: Mel Gorman <mgorman@suse.de>
Cc: Linus Torvalds <torvalds@linux-foundation.org>,
Alex Shi <alex.shi@linaro.org>,
Thomas Gleixner <tglx@linutronix.de>,
Andrew Morton <akpm@linux-foundation.org>,
Fengguang Wu <fengguang.wu@intel.com>,
H Peter Anvin <hpa@zytor.com>, Linux-X86 <x86@kernel.org>,
Linux-MM <linux-mm@kvack.org>,
LKML <linux-kernel@vger.kernel.org>,
Peter Zijlstra <a.p.zijlstra@chello.nl>
Subject: Re: [PATCH 0/4] Fix ebizzy performance regression due to X86 TLB range flush v2
Date: Mon, 16 Dec 2013 14:44:49 +0100 [thread overview]
Message-ID: <20131216134449.GA3034@gmail.com> (raw)
In-Reply-To: <20131216125923.GS11295@suse.de>
* Mel Gorman <mgorman@suse.de> wrote:
> > Whatever we did right in v3.4 we want to do in v3.13 as well - or
> > at least understand it.
>
> Also agreed. I started a bisection before answering this mail. It
> would be cooler and potentially faster to figure it out from direct
> analysis but bisection is reliable and less guesswork.
Trying to guess can potentially last a _lot_ longer than a generic,
no-assumptions bisection ...
The symptoms could point to anything: scheduler, locking details, some
stupid little change in a wakeup sequence somewhere, etc.
It might even be a non-deterministic effect of some timing change
causing the workload 'just' to avoid a common point of preemption and
not scheduling as much - and become more unfair and thus certain
threads lasting longer to finish.
Does the benchmark execute a fixed amount of transactions per thread?
That might artificially increase the numeric regression: with more
threads it 'magnifies' any unfairness effects because slower threads
will become slower, faster threads will become faster, as the thread
count increases.
[ That in itself is somewhat artificial, because real workloads tend
to balance between threads dynamically and don't insist on keeping
the fastest threads idle near the end of a run. It does not
invalidate the complaint about the unfairness itself, obviously. ]
Ingo
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next prev parent reply other threads:[~2013-12-16 13:44 UTC|newest]
Thread overview: 36+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-12-13 20:01 [PATCH 0/4] Fix ebizzy performance regression due to X86 TLB range flush v2 Mel Gorman
2013-12-13 20:01 ` [PATCH 1/4] x86: mm: Clean up inconsistencies when flushing TLB ranges Mel Gorman
2013-12-13 20:01 ` [PATCH 2/4] x86: mm: Account for TLB flushes only when debugging Mel Gorman
2013-12-13 20:01 ` [PATCH 3/4] x86: mm: Change tlb_flushall_shift for IvyBridge Mel Gorman
2013-12-13 20:01 ` [PATCH 4/4] x86: mm: Eliminate redundant page table walk during TLB range flushing Mel Gorman
2013-12-13 21:16 ` [PATCH 0/4] Fix ebizzy performance regression due to X86 TLB range flush v2 Linus Torvalds
2013-12-13 22:38 ` H. Peter Anvin
2013-12-16 10:39 ` Mel Gorman
2013-12-16 17:17 ` Linus Torvalds
2013-12-17 9:55 ` Mel Gorman
2013-12-15 15:55 ` Mel Gorman
2013-12-15 16:17 ` Mel Gorman
2013-12-15 18:34 ` Linus Torvalds
2013-12-16 11:16 ` Mel Gorman
2013-12-16 10:24 ` Ingo Molnar
2013-12-16 12:59 ` Mel Gorman
2013-12-16 13:44 ` Ingo Molnar [this message]
2013-12-17 9:21 ` Mel Gorman
2013-12-17 9:26 ` Peter Zijlstra
2013-12-17 11:00 ` Ingo Molnar
2013-12-17 14:32 ` Mel Gorman
2013-12-17 14:42 ` Ingo Molnar
2013-12-17 17:54 ` Mel Gorman
2013-12-18 10:24 ` Ingo Molnar
2013-12-19 14:24 ` Mel Gorman
2013-12-19 16:49 ` Ingo Molnar
2013-12-20 11:13 ` Mel Gorman
2013-12-20 11:18 ` Ingo Molnar
2013-12-20 12:00 ` Mel Gorman
2013-12-20 12:20 ` Ingo Molnar
2013-12-20 13:55 ` Mel Gorman
2013-12-18 7:28 ` Fengguang Wu
2013-12-19 14:34 ` Mel Gorman
2013-12-20 15:51 ` Fengguang Wu
2013-12-20 16:44 ` Mel Gorman
2013-12-21 15:49 ` Fengguang Wu
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