From: Roman Kagan <rkagan@virtuozzo.com>
To: Paolo Bonzini <pbonzini@redhat.com>
Cc: <linux-kernel@vger.kernel.org>, <kvm@vger.kernel.org>,
<mnghuan@gmail.com>, <luto@kernel.org>
Subject: Re: [PATCH] pvclock: introduce seqcount-like API
Date: Thu, 9 Jun 2016 16:35:29 +0300 [thread overview]
Message-ID: <20160609133529.GA5400@rkaganb.sw.ru> (raw)
In-Reply-To: <db49ab8a-a7be-4550-85b4-f4322ac9300a@redhat.com>
On Thu, Jun 09, 2016 at 02:47:54PM +0200, Paolo Bonzini wrote:
> On 09/06/2016 14:43, Roman Kagan wrote:
> > On Thu, Jun 09, 2016 at 01:23:23PM +0200, Paolo Bonzini wrote:
> >> The version field in struct pvclock_vcpu_time_info basically implements
> >> a seqcount. Wrap it with the usual read_begin and read_retry functions,
> >> and use these APIs instead of peppering the code with smp_rmb()s.
> >> While at it, change it to the more pedantically correct virt_rmb().
> >>
> >> With this change, __pvclock_read_cycles can be simplified noticeably.
> >>
> >> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
> >> ---
> >> arch/x86/entry/vdso/vclock_gettime.c | 25 +++++------------------
> >> arch/x86/include/asm/pvclock.h | 39 +++++++++++++++++++++---------------
> >> arch/x86/kernel/pvclock.c | 17 ++++++----------
> >> 3 files changed, 34 insertions(+), 47 deletions(-)
> > [...]
> >> --- a/arch/x86/include/asm/pvclock.h
> >> +++ b/arch/x86/include/asm/pvclock.h
> > [...]
> >> @@ -69,23 +87,12 @@ static inline u64 pvclock_scale_delta(u64 delta, u32 mul_frac, int shift)
> >> }
> >>
> >> static __always_inline
> >> -unsigned __pvclock_read_cycles(const struct pvclock_vcpu_time_info *src,
> >> - cycle_t *cycles, u8 *flags)
> >> +cycle_t __pvclock_read_cycles(const struct pvclock_vcpu_time_info *src)
> >> {
> >> - unsigned version;
> >> - cycle_t offset;
> >> - u64 delta;
> >> -
> >> - version = src->version;
> >> - /* Make the latest version visible */
> >> - smp_rmb();
> >
> > This is on top of Minfei's patch, right? It isn't in Linus' tree yet so
> > I wonder if it makes sense to merge the two patches into one.
> >
> > Will you post it to stable, too?
>
> Not this one, because Minfei's patch is enough to fix the bug, but I do
Has it landed in any public tree? I'm unable to find any. There
appears to be another version of the patch on the list, so I'm confused.
Roman.
next prev parent reply other threads:[~2016-06-09 13:35 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 [this message]
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
2016-06-12 10:25 ` Minfei Huang
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