From: Davide Libenzi <davidel@xmailserver.org>
To: "Michael S. Tsirkin" <mst@redhat.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>, Avi Kivity <avi@redhat.com>,
gleb@redhat.com, kvm@vger.kernel.org,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 0/2] eventfd: new EFD_STATE flag
Date: Thu, 27 Aug 2009 07:38:46 -0700 (PDT) [thread overview]
Message-ID: <alpine.DEB.2.00.0908270732470.3809@makko.or.mcafeemobile.com> (raw)
In-Reply-To: <20090827143027.GA22720@redhat.com>
On Thu, 27 Aug 2009, Michael S. Tsirkin wrote:
> On Thu, Aug 27, 2009 at 07:21:49AM -0700, Davide Libenzi wrote:
> > On Thu, 27 Aug 2009, Paolo Bonzini wrote:
> >
> > > > Ok, so why not using the eventfd counter as state?
> > > > On the device side:
> > > >
> > > > void write_state(int sfd, int state) {
> > > > u64 cnt;
> > > >
> > > > /* Clear the current state, sfd is in non-blocking mode */
> > > > read(sfd,&cnt, sizeof(cnt));
> > > > /* Writes new state */
> > > > cnt = 1 + !!state;
> > > > write(sfd,&cnt, sizeof(cnt));
> > > > }
> > >
> > > It's interesting [no sarcasm intended, mind] that EFD_SEMAPHORE was
> > > added exactly to avoid a read+write combination for the case of
> > > decrementing a value.
> >
> > Like I repeated 25 times already, EFD_SEMAPHORE was added, because a
> > *semaphore* is a pretty widely known and used abstraction.
>
> what about an atomic variable, btw? does it make sense to implement
> write that does compare and exchange?
It is surprising to me, that is front of a workable solution w/out any
use-once additions, yet you want to try to add optimizations and new
ad-hoc abstractions to user visible interfaces.
Now, you tell me what an atomic variable has to do with an eventfd.
- Davide
next prev parent reply other threads:[~2009-08-27 14:38 UTC|newest]
Thread overview: 79+ messages / expand[flat|nested] mbox.gz Atom feed top
2009-08-20 15:56 [PATCH 0/2] eventfd: new EFD_STATE flag Michael S. Tsirkin
2009-08-20 16:20 ` Davide Libenzi
2009-08-20 17:38 ` Avi Kivity
2009-08-20 17:44 ` Davide Libenzi
2009-08-20 17:56 ` Paolo Bonzini
2009-08-21 17:21 ` Davide Libenzi
2009-08-20 17:55 ` Michael S. Tsirkin
2009-08-20 18:06 ` Avi Kivity
2009-08-20 18:28 ` Michael S. Tsirkin
2009-08-23 13:01 ` Avi Kivity
2009-08-23 13:36 ` Michael S. Tsirkin
2009-08-23 13:40 ` Avi Kivity
2009-08-23 14:30 ` Michael S. Tsirkin
2009-08-23 16:51 ` Paolo Bonzini
2009-08-24 18:25 ` Davide Libenzi
2009-08-24 18:31 ` Avi Kivity
2009-08-24 22:08 ` Davide Libenzi
2009-08-24 22:10 ` Paolo Bonzini
2009-08-24 22:32 ` Davide Libenzi
2009-08-25 6:59 ` Paolo Bonzini
2009-08-25 4:26 ` Avi Kivity
2009-08-24 21:49 ` Michael S. Tsirkin
2009-08-24 22:15 ` Davide Libenzi
2009-08-25 7:22 ` Michael S. Tsirkin
2009-08-25 21:57 ` Davide Libenzi
2009-08-26 10:29 ` Michael S. Tsirkin
2009-08-26 10:41 ` Avi Kivity
2009-08-26 17:45 ` Davide Libenzi
2009-08-26 18:58 ` Avi Kivity
2009-08-26 19:13 ` Davide Libenzi
2009-08-26 19:42 ` Avi Kivity
2009-08-26 19:44 ` Davide Libenzi
2009-08-26 23:30 ` Davide Libenzi
2009-08-27 4:13 ` Avi Kivity
2009-08-27 8:06 ` Michael S. Tsirkin
2009-08-27 14:20 ` Davide Libenzi
2009-08-26 19:50 ` Gleb Natapov
2009-08-26 20:04 ` Davide Libenzi
2009-08-27 5:25 ` Gleb Natapov
2009-08-27 9:05 ` Paolo Bonzini
2009-08-27 9:09 ` Michael S. Tsirkin
2009-08-27 14:21 ` Davide Libenzi
2009-08-27 14:30 ` Michael S. Tsirkin
2009-08-27 14:38 ` Davide Libenzi [this message]
2009-08-27 14:49 ` Michael S. Tsirkin
2009-08-27 15:29 ` Davide Libenzi
2009-08-27 17:09 ` Davide Libenzi
[not found] ` <alpine.DEB.2.00.0908311644410.17349@makko.or.mcafeemobile.com>
[not found] ` <4A9CB318.7030401@redhat.com>
[not found] ` <alpine.DEB.2.00.0909010723380.28172@makko.or.mcafeemobile.com>
2010-01-06 19:33 ` Michael S. Tsirkin
2010-01-06 20:43 ` Davide Libenzi
2010-01-06 20:55 ` Michael S. Tsirkin
2010-01-06 21:17 ` Davide Libenzi
2010-01-06 22:29 ` Michael S. Tsirkin
2010-01-06 22:46 ` Davide Libenzi
2010-01-06 23:45 ` Michael S. Tsirkin
2010-01-06 23:59 ` Davide Libenzi
2010-01-07 0:02 ` Michael S. Tsirkin
2010-01-07 6:45 ` Michael S. Tsirkin
2010-01-07 7:25 ` Davide Libenzi
2010-01-07 10:36 ` Michael S. Tsirkin
2010-01-07 23:37 ` Davide Libenzi
2010-01-08 0:13 ` Davide Libenzi
2010-01-08 0:26 ` Davide Libenzi
2010-01-10 10:30 ` Michael S. Tsirkin
2010-01-10 15:26 ` Davide Libenzi
2010-01-10 16:22 ` Michael S. Tsirkin
2010-01-10 17:27 ` Davide Libenzi
2010-01-10 17:35 ` Michael S. Tsirkin
2010-01-10 19:04 ` Davide Libenzi
2010-01-11 7:34 ` Michael S. Tsirkin
2010-01-11 19:14 ` Davide Libenzi
2010-01-11 19:19 ` Michael S. Tsirkin
2010-01-11 22:53 ` Davide Libenzi
2010-01-13 17:07 ` Michael S. Tsirkin
2010-01-11 9:01 ` Gleb Natapov
2010-01-11 9:02 ` Michael S. Tsirkin
2010-01-11 9:08 ` Gleb Natapov
2010-01-11 9:19 ` Michael S. Tsirkin
2010-01-11 9:36 ` Gleb Natapov
2010-01-11 9:41 ` Michael S. Tsirkin
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