[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Message-ID: <CALCETrX3_AwH7f4uXp9-casxc9_OB35SvFE9ahGq+yYKPZh04A@mail.gmail.com>
Date: Sat, 9 Jan 2016 14:36:03 -0800
From: Andy Lutomirski <luto@...capital.net>
To: Chris Wilson <chris@...is-wilson.co.uk>,
"H. Peter Anvin" <hpa@...or.com>,
Andy Lutomirski <luto@...capital.net>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
Ross Zwisler <ross.zwisler@...ux.intel.com>,
"H . Peter Anvin" <hpa@...ux.intel.com>,
Borislav Petkov <bp@...en8.de>,
Brian Gerst <brgerst@...il.com>,
Denys Vlasenko <dvlasenk@...hat.com>,
Linus Torvalds <torvalds@...ux-foundation.org>,
Thomas Gleixner <tglx@...utronix.de>,
Imre Deak <imre.deak@...el.com>,
Daniel Vetter <daniel.vetter@...ll.ch>,
DRI <dri-devel@...ts.freedesktop.org>
Subject: Re: [PATCH] x86: Add an explicit barrier() to clflushopt()
On Sat, Jan 9, 2016 at 12:01 AM, Chris Wilson <chris@...is-wilson.co.uk> wrote:
> On Thu, Jan 07, 2016 at 02:32:23PM -0800, H. Peter Anvin wrote:
>> On 01/07/16 14:29, H. Peter Anvin wrote:
>> >
>> > I would be very interested in knowing if replacing the final clflushopt
>> > with a clflush would resolve your problems (in which case the last mb()
>> > shouldn't be necessary either.)
>> >
>>
>> Nevermind. CLFLUSH is not ordered with regards to CLFLUSHOPT to the
>> same cache line.
>>
>> Could you add a sync_cpu(); call to the end (can replace the final mb())
>> and see if that helps your case?
>
> s/sync_cpu()/sync_core()/
>
> No. I still see failures on Baytrail and Braswell (Pineview is not
> affected) with the final mb() replaced with sync_core(). I can reproduce
> failures on Pineview by tweaking the clflush_cache_range() parameters,
> so I am fairly confident that it is validating the current code.
>
> iirc sync_core() is cpuid, a heavy serialising instruction, an
> alternative to mfence. Is there anything that else I can infer about
> the nature of my bug from this result?
No clue, but I don't know much about the underlying architecture.
Can you try clflush_cache_ranging one cacheline less and then manually
doing clflushopt; mb on the last cache line, just to make sure that
the helper is really doing the right thing? You could also try
clflush instead of clflushopt to see if that makes a difference.
--Andy
--
Andy Lutomirski
AMA Capital Management, LLC
Powered by blists - more mailing lists