From: "Michael S. Tsirkin" <mst@redhat.com>
To: Takuya Yoshikawa <yoshikawa.takuya@oss.ntt.co.jp>
Cc: Takuya Yoshikawa <takuya.yoshikawa@gmail.com>,
Marcelo Tosatti <mtosatti@redhat.com>,
avi@redhat.com, kvm@vger.kernel.org
Subject: Re: [PATCH -v3] KVM: x86: lapic: Clean up find_highest_vector() and count_vectors()
Date: Wed, 5 Sep 2012 12:51:27 +0300 [thread overview]
Message-ID: <20120905095126.GA10531@redhat.com> (raw)
In-Reply-To: <20120905184026.9aeddbc1.yoshikawa.takuya@oss.ntt.co.jp>
On Wed, Sep 05, 2012 at 06:40:26PM +0900, Takuya Yoshikawa wrote:
> On Wed, 5 Sep 2012 12:26:49 +0300
> "Michael S. Tsirkin" <mst@redhat.com> wrote:
>
> > It's not guaranteed if another thread can modify the bitmap.
> > Is this the case here? If yes we need at least ACCESS_ONCE.
>
> In this patch, using the wrapper function to read out a register
> value forces compilers not to do bad things.
It's not robust. Compiler is free to optimize it out, and it
frequently does that.
> But I agree that it is not a good API.
>
> I would like to use fls() rather than ACCESS_ONCE if it's
> really needed.
Sure, makes sense.
> > > Anyway, I'm now thinking that we do not care about such
> > > things here, and can just follow your advice, yes?
> >
> > Unless you see an issue with it ...
>
> Although I read the code, I'm not sure.
>
> But this code is apparently not so critical for performance
> that we can simply use fls().
Yes. I guess if it becomes critical we'll need to add a cache anyway.
> If I can remove likely() and use proper macros, that's enough
> for me.
Me too.
> Thanks,
> Takuya
next prev parent reply other threads:[~2012-09-05 9:50 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-08-24 9:15 [PATCH] KVM: x86: lapic: Fix the misuse of likely() in find_highest_vector() Takuya Yoshikawa
2012-08-27 20:25 ` Marcelo Tosatti
2012-08-28 9:57 ` Takuya Yoshikawa
2012-08-29 19:10 ` Marcelo Tosatti
2012-08-29 22:51 ` Michael S. Tsirkin
2012-08-30 1:09 ` Takuya Yoshikawa
2012-08-30 6:37 ` Michael S. Tsirkin
2012-08-30 9:50 ` Takuya Yoshikawa
2012-08-30 10:10 ` Michael S. Tsirkin
2012-08-30 10:24 ` Takuya Yoshikawa
2012-08-30 10:44 ` Michael S. Tsirkin
2012-08-30 12:30 ` [PATCH -v3] KVM: x86: lapic: Clean up find_highest_vector() and count_vectors() Takuya Yoshikawa
2012-08-30 13:21 ` Michael S. Tsirkin
2012-08-30 16:09 ` Takuya Yoshikawa
2012-08-30 16:49 ` Michael S. Tsirkin
2012-09-05 8:30 ` Takuya Yoshikawa
2012-09-05 9:26 ` Michael S. Tsirkin
2012-09-05 9:40 ` Takuya Yoshikawa
2012-09-05 9:51 ` Michael S. Tsirkin [this message]
2012-09-05 10:30 ` [PATCH -v4] " Takuya Yoshikawa
2012-09-05 10:58 ` Michael S. Tsirkin
2012-09-12 16:39 ` Marcelo Tosatti
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