From: Andrew Morton <akpm@linux-foundation.org>
To: Christoph Lameter <cl@linux.com>
Cc: "Nicholas A. Bellinger" <nab@linux-iscsi.org>,
Kent Overstreet <kmo@daterainc.com>,
linux-kernel@vger.kernel.org, Tejun Heo <tj@kernel.org>,
Oleg Nesterov <oleg@redhat.com>, Ingo Molnar <mingo@redhat.com>,
Andi Kleen <andi@firstfloor.org>, Jens Axboe <axboe@kernel.dk>
Subject: Re: [PATCH] idr: Use this_cpu_ptr() for percpu_ida
Date: Wed, 21 Aug 2013 13:49:45 -0700 [thread overview]
Message-ID: <20130821134945.16b32c045e28272c5b0ba610@linux-foundation.org> (raw)
In-Reply-To: <00000140a14ae6bb-f0fca267-cdd6-4039-8c6b-f715999a83c5-000000@email.amazonses.com>
On Wed, 21 Aug 2013 14:32:55 +0000 Christoph Lameter <cl@linux.com> wrote:
> On Tue, 20 Aug 2013, Nicholas A. Bellinger wrote:
>
> > On Thu, 2013-08-08 at 14:32 +0000, Christoph Lameter wrote:
> > > On Wed, 7 Aug 2013, Kent Overstreet wrote:
> > >
> > > > One thing that was bugging me - I was never able to figure out for sure
> > > > if smp_processor_id() returns a number in the range [0, nr_cpu_ids), at
> > > > least I couldn't find where it was documented - could you tell me if
> > > > that's true?
> > >
> > > I always assumed that it was in the range 0 ... nr_cpu_ids - 1 and that is
> > > the assumption under which the kernel code was written. Things would break
> > > horribly if smp_process_id would return nr_cpu_ids or higher.
> > >
> >
> > Hi guys,
> >
> > Just a heads up that I've put Kent's standalone percpu-ida patch (with
> > Christoph's recommend changes) into target-pending/for-next here:
> >
> > https://git.kernel.org/cgit/linux/kernel/git/nab/target-pending.git/commit/?h=for-next&id=47bd524a5b3eb6429b058b8b562b45329ab2c9e7
> >
> > I've got a number of target patches that depend on this code for v3.12,
> > and a delay on this particular piece would be painful to endure..
> >
> > Sooo, please yell loudly if there is an objection to percpu-ida merge as
> > a completely standalone item, that does not effect any existing ida
> > code.
>
> Well the performance is still going to be limited due to the spinlock in
> the percpu handling. You do not need the spinlock. Once preempt is off you
> should have exclusive access to the per cpu data.
The lock is needed so that one cpu can steal tags from another cpu's cache.
See (the needlessly inlined!) steal_tags().
next prev parent reply other threads:[~2013-08-21 20:49 UTC|newest]
Thread overview: 40+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-08-07 17:34 IDA/IDR rewrite, percpu ida Kent Overstreet
2013-08-07 17:34 ` [PATCH 03/10] idr: Rewrite ida Kent Overstreet
2013-08-07 20:22 ` Tejun Heo
2013-08-07 20:51 ` [PATCH] idr: Document ida tree sections Kent Overstreet
2013-08-09 14:57 ` Tejun Heo
2013-08-13 22:13 ` Kent Overstreet
2013-08-13 22:19 ` Tejun Heo
2013-08-13 22:27 ` Kent Overstreet
2013-08-13 22:44 ` Tejun Heo
2013-08-13 22:59 ` Kent Overstreet
2013-08-13 23:22 ` Tejun Heo
2013-08-13 23:51 ` Kent Overstreet
2013-08-13 23:59 ` Tejun Heo
2013-08-15 0:04 ` Kent Overstreet
2013-08-15 0:22 ` Tejun Heo
2013-08-13 22:33 ` Kent Overstreet
2013-08-07 17:34 ` [PATCH 04/10] idr: Percpu ida Kent Overstreet
2013-08-07 17:56 ` Christoph Lameter
2013-08-07 18:33 ` Kent Overstreet
2013-08-07 19:40 ` Christoph Lameter
2013-08-07 19:57 ` [PATCH] idr: Use this_cpu_ptr() for percpu_ida Kent Overstreet
2013-08-08 14:32 ` Christoph Lameter
2013-08-20 21:19 ` Nicholas A. Bellinger
2013-08-20 21:29 ` Andrew Morton
2013-08-21 2:01 ` Kent Overstreet
2013-08-21 2:07 ` Tejun Heo
2013-08-21 2:31 ` Kent Overstreet
2013-08-21 11:59 ` Tejun Heo
2013-08-21 21:09 ` Kent Overstreet
2013-08-21 21:16 ` Tejun Heo
2013-08-21 21:24 ` Kent Overstreet
2013-08-21 21:31 ` Tejun Heo
2013-08-21 14:32 ` Christoph Lameter
2013-08-21 17:49 ` Nicholas A. Bellinger
2013-08-21 20:49 ` Andrew Morton [this message]
2013-08-22 16:44 ` Christoph Lameter
2013-08-22 16:56 ` Jens Axboe
2013-08-07 17:46 ` [PATCH 05/10] idr: Kill old deprecated idr interfaces Kent Overstreet
2013-08-07 17:46 ` [PATCH 06/10] idr: Rename idr_get_next() -> idr_find_next() Kent Overstreet
2013-08-07 17:46 ` [PATCH 08/10] idr: Reimplement idr on top of ida/radix trees Kent Overstreet
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