From: Peter Zijlstra <peterz@infradead.org>
To: Waiman Long <waiman.long@hpe.com>
Cc: Ingo Molnar <mingo@redhat.com>,
linux-kernel@vger.kernel.org,
Scott J Norton <scott.norton@hpe.com>,
Douglas Hatch <doug.hatch@hpe.com>, Paul Turner <pjt@google.com>,
Ben Segall <bsegall@google.com>,
Morten Rasmussen <morten.rasmussen@arm.com>,
Yuyang Du <yuyang.du@intel.com>
Subject: Re: [RFC PATCH 3/3] sched/fair: Use different cachelines for readers and writers of load_avg
Date: Mon, 30 Nov 2015 23:29:36 +0100 [thread overview]
Message-ID: <20151130222936.GF3816@twins.programming.kicks-ass.net> (raw)
In-Reply-To: <565C9FDC.9020603@hpe.com>
On Mon, Nov 30, 2015 at 02:13:32PM -0500, Waiman Long wrote:
> >This would only work if the structure itself is allocated with cacheline
> >alignment, and looking at sched_create_group(), we use a plain kzalloc()
> >for this, which doesn't guarantee any sort of alignment beyond machine
> >word size IIRC.
>
> With a RHEL 6 derived .config file, the size of the task_group structure was
> 460 bytes on a 32-bit x86 kernel. Adding a ____cacheline_aligned tag
> increase the size to 512 bytes. So it did make the structure a multiple of
> the cacheline size. With both slub and slab, the allocated task group
> pointers from kzalloc() in sched_create_group() were all multiples of 0x200.
> So they were properly aligned for the ____cacheline_aligned tag to work.
Not sure we should rely on sl*b doing the right thing here.
KMALLOC_MIN_ALIGN is explicitly set to sizeof(long long). If you want
explicit alignment, one should use KMEM_CACHE().
next prev parent reply other threads:[~2015-11-30 22:29 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-11-25 19:09 [PATCH 0/3] sched/fair: Reduce contention on tg's load_avg Waiman Long
2015-11-25 19:09 ` [PATCH 1/3] sched/fair: Avoid redundant idle_cpu() call in update_sg_lb_stats() Waiman Long
2015-12-04 11:57 ` [tip:sched/core] " tip-bot for Waiman Long
2015-11-25 19:09 ` [PATCH 2/3] sched/fair: Move hot load_avg into its own cacheline Waiman Long
2015-11-30 10:23 ` Peter Zijlstra
2015-11-25 19:09 ` [RFC PATCH 3/3] sched/fair: Use different cachelines for readers and writers of load_avg Waiman Long
2015-11-30 10:22 ` Peter Zijlstra
2015-11-30 19:13 ` Waiman Long
2015-11-30 22:09 ` Peter Zijlstra
2015-12-01 3:55 ` Waiman Long
2015-12-01 8:49 ` Peter Zijlstra
2015-12-01 10:44 ` Mike Galbraith
2015-12-02 18:48 ` Waiman Long
2015-11-30 22:29 ` Peter Zijlstra [this message]
2015-12-01 4:00 ` Waiman Long
2015-12-01 8:47 ` Peter Zijlstra
2015-12-02 18:44 ` Waiman Long
2015-11-30 22:32 ` Peter Zijlstra
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