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Re: [Qemu-devel] [PATCH 07/12] qemu-thread: add QemuSemaphore
From: |
Paolo Bonzini |
Subject: |
Re: [Qemu-devel] [PATCH 07/12] qemu-thread: add QemuSemaphore |
Date: |
Mon, 16 Jul 2012 15:20:16 +0200 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:13.0) Gecko/20120615 Thunderbird/13.0.1 |
Il 16/07/2012 14:00, Jan Kiszka ha scritto:
> On 2012-07-16 12:42, Paolo Bonzini wrote:
>> The new thread pool will use semaphores instead of condition
>> variables, because QemuCond does not have qemu_cond_timedwait.
>
> I'll post an updated patch (according to last round's review comments)
> that adds this service for POSIX. I bet you'll find a way to extend it
> to Win32 if that is required. ;)
I can do that (or just use pthreads-win32), but only at the cost of
making cond_wait() slower and more complex.
>> (I also like it more this way, since semaphores model well the
>> producer-consumer problem).
>
> Let's not introduce another synchronization mechanism unless there is a
> real need. Semaphores tend to be misused for things they don't fit, so
> better keep them out of reach.
That's what patch review is for...
> Also, if you do producer-consumer this way, you need a down() for every
> entity you dequeue. In contrast, you only interact with condition
> variables if there the consumer queue is empty - less atomic ops.
It doesn't really matter. You want the thread pool to service requests
as fast as possible, which means you'll have always at least one free
thread waiting on the semaphore or cv. So, with either semaphores or
cvs, the slow path is actually the normal case.
Paolo
- [Qemu-devel] [PATCH 02/12] event_notifier: add Win32 implementation, (continued)
- [Qemu-devel] [PATCH 02/12] event_notifier: add Win32 implementation, Paolo Bonzini, 2012/07/16
- [Qemu-devel] [PATCH 04/12] aio: provide platform-independent API, Paolo Bonzini, 2012/07/16
- [Qemu-devel] [PATCH 03/12] main-loop: use event notifiers, Paolo Bonzini, 2012/07/16
- [Qemu-devel] [PATCH 05/12] aio: add Win32 implementation, Paolo Bonzini, 2012/07/16
- [Qemu-devel] [PATCH 06/12] linux-aio: use event notifiers, Paolo Bonzini, 2012/07/16
- [Qemu-devel] [PATCH 07/12] qemu-thread: add QemuSemaphore, Paolo Bonzini, 2012/07/16
- Re: [Qemu-devel] [PATCH 07/12] qemu-thread: add QemuSemaphore, Jan Kiszka, 2012/07/16
- [Qemu-devel] [PATCH] qemu-thread: Introduce qemu_cond_timedwait for POSIX, Jan Kiszka, 2012/07/16
- Re: [Qemu-devel] [PATCH 07/12] qemu-thread: add QemuSemaphore,
Paolo Bonzini <=
- Re: [Qemu-devel] [PATCH 07/12] qemu-thread: add QemuSemaphore, Jan Kiszka, 2012/07/16
- Re: [Qemu-devel] [PATCH 07/12] qemu-thread: add QemuSemaphore, Paolo Bonzini, 2012/07/16
- Re: [Qemu-devel] [PATCH 07/12] qemu-thread: add QemuSemaphore, Jan Kiszka, 2012/07/16
- Re: [Qemu-devel] [PATCH 07/12] qemu-thread: add QemuSemaphore, Paolo Bonzini, 2012/07/16
- Re: [Qemu-devel] [PATCH 07/12] qemu-thread: add QemuSemaphore, Jan Kiszka, 2012/07/16
- Re: [Qemu-devel] [PATCH 07/12] qemu-thread: add QemuSemaphore, Paolo Bonzini, 2012/07/16
- Re: [Qemu-devel] [PATCH 07/12] qemu-thread: add QemuSemaphore, Paolo Bonzini, 2012/07/24
[Qemu-devel] [PATCH 08/12] aio: add generic thread-pool facility, Paolo Bonzini, 2012/07/16
[Qemu-devel] [PATCH 10/12] raw: merge posix-aio-compat.c into block/raw-posix.c, Paolo Bonzini, 2012/07/16
[Qemu-devel] [PATCH 11/12] raw-posix: rename raw-posix-aio.h, hide unavailable prototypes, Paolo Bonzini, 2012/07/16