From: Paolo Bonzini <pbonzini@redhat.com>
To: Andy Lutomirski <luto@amacapital.net>
Cc: Roman Kagan <rkagan@virtuozzo.com>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
kvm list <kvm@vger.kernel.org>, Minfei Huang <mnghuan@gmail.com>,
Andrew Lutomirski <luto@kernel.org>
Subject: Re: [PATCH] pvclock: introduce seqcount-like API
Date: Wed, 15 Jun 2016 14:17:09 +0200 [thread overview]
Message-ID: <d212c92f-3742-de4e-132f-f2311a8ba0aa@redhat.com> (raw)
In-Reply-To: <CALCETrVnN25Oza+-UQouc_pXD-W+A=d7SNLwCpih8BJxe=GL8Q@mail.gmail.com>
On 09/06/2016 20:08, Andy Lutomirski wrote:
> > __pvclock_read_cycles is pretty much the same as the code that is being
> > inlined. Thus the only change is that __pvclock_read_cycles is called
> > inside the loop rather than outside, but the loop really is expected to
> > never roll so why make a copy in the first place?
>
> I feel like I had a reason, but I don't remember what it was.
I cannot see any substantial difference in the generated code with
this patch. On the other hand, if I add this:
diff --git a/arch/x86/include/asm/pvclock.h b/arch/x86/include/asm/pvclock.h
index 0ee92db1e9f3..d019f0cc80ec 100644
--- a/arch/x86/include/asm/pvclock.h
+++ b/arch/x86/include/asm/pvclock.h
@@ -40,7 +40,7 @@ bool pvclock_read_retry(const struct pvclock_vcpu_time_info *src,
{
/* Make sure that the version is re-read after the data. */
virt_rmb();
- return version != src->version;
+ return unlikely(version != src->version);
}
/*
then vread_pvclock is inlined everywhere, which bloats the code somewhat (+80
code bytes). Do you want me to mark vread_pvclock as noinline too?
Paolo
next prev parent reply other threads:[~2016-06-15 12:17 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-06-09 11:23 [PATCH] pvclock: introduce seqcount-like API Paolo Bonzini
2016-06-09 12:43 ` Roman Kagan
2016-06-09 12:47 ` Paolo Bonzini
2016-06-09 13:35 ` Roman Kagan
2016-06-09 13:45 ` Paolo Bonzini
2016-06-09 17:12 ` Andy Lutomirski
2016-06-09 18:03 ` Paolo Bonzini
2016-06-09 18:08 ` Andy Lutomirski
2016-06-15 12:17 ` Paolo Bonzini [this message]
2016-06-12 10:25 ` Minfei Huang
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