From: Peter Zijlstra <peterz@infradead.org>
To: Suresh Siddha <suresh.b.siddha@intel.com>
Cc: Venkatesh Pallipadi <venki@google.com>,
Ingo Molnar <mingo@elte.hu>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
Paul Turner <pjt@google.com>, Mike Galbraith <efault@gmx.de>,
Nick Piggin <npiggin@gmail.com>
Subject: Re: [PATCH] sched: Resolve sd_idle and first_idle_cpu Catch-22 - v1
Date: Wed, 09 Feb 2011 16:55:28 +0100 [thread overview]
Message-ID: <1297266928.13327.216.camel@laptop> (raw)
In-Reply-To: <1297108399.8221.35.camel@sbsiddha-MOBL3.sc.intel.com>
On Mon, 2011-02-07 at 11:53 -0800, Suresh Siddha wrote:
>
> Peter, to answer your question of why SMT is treated different to cores
> sharing cache, performance improvements contributed by SMT is far less
> compared to the cores and any wrong decisions in SMT load balancing
> (especially in the presence of idle cores, packages) has a bigger
> impact.
>
> I think in the tbench case referred by Nick, idle HT siblings in a busy
> package picked the load instead of the idle packages. And thus we
> probably had to wait for active load balance to kick in to distribute
> the load etc by which the damage would have been. Performance impact of
> this condition wouldn't be as severe in the cores sharing last level
> cache and other resources.
>
> Also there are lot of changes in this area since 2005. So it would be
> nice to revisit the tbench case and see if the logic of propagating busy
> sibling status to the higher level load balances is still needed or not.
>
> On the contrary, perhaps there might be some workloads which may benefit
> in performance/latency if we completely do away with this less
> aggressive SMT load balancing.
Right, but our current capacity logic does exactly that and seems to
work for more than 2 smt siblings (it does the whole asymmetric power7
muck).
>From a quick glance at the sched.c state at the time of Nick's patch,
the capacity logic wasn't around then.
So I see no reason what so ever to keep this SMT exception.
next prev parent reply other threads:[~2011-02-09 15:54 UTC|newest]
Thread overview: 24+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-02-04 20:51 [PATCH] sched: Resolve sd_idle and first_idle_cpu Catch-22 Venkatesh Pallipadi
2011-02-04 21:25 ` [PATCH] sched: Resolve sd_idle and first_idle_cpu Catch-22 - v1 Venkatesh Pallipadi
2011-02-07 13:50 ` Peter Zijlstra
2011-02-07 18:21 ` Venkatesh Pallipadi
2011-02-07 19:53 ` Suresh Siddha
2011-02-08 17:37 ` Venkatesh Pallipadi
2011-02-08 18:13 ` Misc sd_idle related fixes Venkatesh Pallipadi
2011-02-09 9:29 ` Peter Zijlstra
2011-02-10 17:24 ` Venkatesh Pallipadi
2011-02-08 18:13 ` [PATCH 1/3] sched: Resolve sd_idle and first_idle_cpu Catch-22 Venkatesh Pallipadi
2011-02-08 18:13 ` [PATCH 2/3] sched: fix_up broken SMT load balance dilation Venkatesh Pallipadi
2011-02-08 18:13 ` [PATCH 3/3] sched: newidle balance set idle_timestamp only on successful pull Venkatesh Pallipadi
2011-02-09 3:37 ` Mike Galbraith
2011-02-09 15:55 ` Peter Zijlstra [this message]
2011-02-12 1:20 ` [PATCH] sched: Resolve sd_idle and first_idle_cpu Catch-22 - v1 Suresh Siddha
2011-02-14 22:38 ` [PATCH] sched: Wholesale removal of sd_idle logic Venkatesh Pallipadi
2011-02-15 17:01 ` Vaidyanathan Srinivasan
2011-02-15 18:26 ` Venkatesh Pallipadi
2011-02-16 8:53 ` Vaidyanathan Srinivasan
2011-02-16 11:43 ` Peter Zijlstra
2011-02-16 13:50 ` [tip:sched/core] " tip-bot for Venkatesh Pallipadi
2011-02-15 9:15 ` [PATCH] sched: Resolve sd_idle and first_idle_cpu Catch-22 - v1 Peter Zijlstra
2011-02-15 19:11 ` Suresh Siddha
2011-02-18 1:05 ` Alex,Shi
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