From: "H. Peter Anvin" <hpa@zytor.com>
To: "Michael S. Tsirkin" <mst@redhat.com>,
linux-kernel@vger.kernel.org,
Linus Torvalds <torvalds@linux-foundation.org>
Cc: Davidlohr Bueso <dave@stgolabs.net>,
Davidlohr Bueso <dbueso@suse.de>,
Peter Zijlstra <peterz@infradead.org>,
the arch/x86 maintainers <x86@kernel.org>,
virtualization <virtualization@lists.linux-foundation.org>,
Thomas Gleixner <tglx@linutronix.de>,
"Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
Ingo Molnar <mingo@kernel.org>
Subject: Re: [PATCH v2 0/3] x86: faster mb()+other barrier.h tweaks
Date: Tue, 12 Jan 2016 14:25:24 -0800 [thread overview]
Message-ID: <56957D54.5000602@zytor.com> (raw)
In-Reply-To: <1452635935-5439-1-git-send-email-mst@redhat.com>
On 01/12/16 14:10, Michael S. Tsirkin wrote:
> mb() typically uses mfence on modern x86, but a micro-benchmark shows that it's
> 2 to 3 times slower than lock; addl $0,(%%e/rsp) that we use on older CPUs.
>
> So let's use the locked variant everywhere - helps keep the code simple as
> well.
>
> While I was at it, I found some inconsistencies in comments in
> arch/x86/include/asm/barrier.h
>
> I hope I'm not splitting this up too much - the reason is I wanted to isolate
> the code changes (that people might want to test for performance) from comment
> changes approved by Linus, from (so far unreviewed) comment change I came up
> with myself.
>
> Lightly tested on my system.
>
> Michael S. Tsirkin (3):
> x86: drop mfence in favor of lock+addl
> x86: drop a comment left over from X86_OOSTORE
> x86: tweak the comment about use of wmb for IO
>
I would like to get feedback from the hardware team about the
implications of this change, first.
-hpa
WARNING: multiple messages have this Message-ID (diff)
From: "H. Peter Anvin" <hpa@zytor.com>
To: "Michael S. Tsirkin" <mst@redhat.com>,
linux-kernel@vger.kernel.org,
Linus Torvalds <torvalds@linux-foundation.org>
Cc: Davidlohr Bueso <dave@stgolabs.net>,
Peter Zijlstra <peterz@infradead.org>,
Ingo Molnar <mingo@kernel.org>,
Thomas Gleixner <tglx@linutronix.de>,
"Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
the arch/x86 maintainers <x86@kernel.org>,
Davidlohr Bueso <dbueso@suse.de>,
virtualization <virtualization@lists.linux-foundation.org>
Subject: Re: [PATCH v2 0/3] x86: faster mb()+other barrier.h tweaks
Date: Tue, 12 Jan 2016 14:25:24 -0800 [thread overview]
Message-ID: <56957D54.5000602@zytor.com> (raw)
In-Reply-To: <1452635935-5439-1-git-send-email-mst@redhat.com>
On 01/12/16 14:10, Michael S. Tsirkin wrote:
> mb() typically uses mfence on modern x86, but a micro-benchmark shows that it's
> 2 to 3 times slower than lock; addl $0,(%%e/rsp) that we use on older CPUs.
>
> So let's use the locked variant everywhere - helps keep the code simple as
> well.
>
> While I was at it, I found some inconsistencies in comments in
> arch/x86/include/asm/barrier.h
>
> I hope I'm not splitting this up too much - the reason is I wanted to isolate
> the code changes (that people might want to test for performance) from comment
> changes approved by Linus, from (so far unreviewed) comment change I came up
> with myself.
>
> Lightly tested on my system.
>
> Michael S. Tsirkin (3):
> x86: drop mfence in favor of lock+addl
> x86: drop a comment left over from X86_OOSTORE
> x86: tweak the comment about use of wmb for IO
>
I would like to get feedback from the hardware team about the
implications of this change, first.
-hpa
next prev parent reply other threads:[~2016-01-12 22:25 UTC|newest]
Thread overview: 26+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-01-12 22:10 [PATCH v2 0/3] x86: faster mb()+other barrier.h tweaks Michael S. Tsirkin
2016-01-12 22:10 ` Michael S. Tsirkin
2016-01-12 22:10 ` [PATCH v2 1/3] x86: drop mfence in favor of lock+addl Michael S. Tsirkin
2016-01-12 22:10 ` Michael S. Tsirkin
2016-01-12 22:10 ` [PATCH v2 2/3] x86: drop a comment left over from X86_OOSTORE Michael S. Tsirkin
2016-01-12 22:10 ` Michael S. Tsirkin
2016-01-12 22:25 ` One Thousand Gnomes
2016-01-12 22:25 ` One Thousand Gnomes
2016-01-12 22:10 ` [PATCH v2 3/3] x86: tweak the comment about use of wmb for IO Michael S. Tsirkin
2016-01-12 22:10 ` Michael S. Tsirkin
2016-01-12 22:25 ` H. Peter Anvin [this message]
2016-01-12 22:25 ` [PATCH v2 0/3] x86: faster mb()+other barrier.h tweaks H. Peter Anvin
2016-01-26 8:20 ` Michael S. Tsirkin
2016-01-26 8:20 ` Michael S. Tsirkin
2016-01-26 21:37 ` H. Peter Anvin
2016-01-26 21:37 ` H. Peter Anvin
2016-01-27 14:07 ` Michael S. Tsirkin
2016-01-27 14:07 ` Michael S. Tsirkin
2016-01-27 14:14 ` Peter Zijlstra
2016-01-27 14:14 ` Peter Zijlstra
2016-01-27 14:18 ` Michael S. Tsirkin
2016-01-27 14:18 ` Michael S. Tsirkin
2018-10-11 17:37 ` Andres Freund
2018-10-11 18:11 ` Michael S. Tsirkin
2018-10-11 18:21 ` Andres Freund
2018-10-11 18:11 ` Michael S. Tsirkin
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