From: Avi Kivity <avi@scylladb.com>
To: Paolo Bonzini <pbonzini@redhat.com>,
Stefan Hajnoczi <stefanha@redhat.com>,
linux-fsdevel@vger.kernel.org
Cc: kvm@vger.kernel.org, linux-kernel@vger.kernel.org,
Davide Libenzi <davidel@xmailserver.org>,
Alexander Viro <viro@zeniv.linux.org.uk>
Subject: Re: [RFC] eventfd: add EFD_AUTORESET flag
Date: Wed, 12 Feb 2020 12:10:45 +0200 [thread overview]
Message-ID: <a5299230-4e86-43d1-7f99-cc1f455a39c7@scylladb.com> (raw)
In-Reply-To: <66566792-58a4-bf65-6723-7d2887c84160@redhat.com>
On 12/02/2020 10.31, Paolo Bonzini wrote:
> On 29/01/20 18:20, Stefan Hajnoczi wrote:
>> + /* Semaphore semantics don't make sense when autoreset is enabled */
>> + if ((flags & EFD_SEMAPHORE) && (flags & EFD_AUTORESET))
>> + return -EINVAL;
>> +
> I think they do, you just want to subtract 1 instead of setting the
> count to 0. This way, writing 1 would be the post operation on the
> semaphore, while poll() would be the wait operation.
poll() is usually idempotent. Both resetting to zero and subtracting one
goes against the grain.
Better to use uring async read. This way you get the value just as you
do with with poll+read, and the syscall cost is amortized away by uring.
next prev parent reply other threads:[~2020-02-12 10:10 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-01-29 17:20 [RFC] eventfd: add EFD_AUTORESET flag Stefan Hajnoczi
2020-02-04 15:40 ` Stefan Hajnoczi
2020-02-11 9:32 ` Stefan Hajnoczi
2020-02-12 8:31 ` Paolo Bonzini
2020-02-12 10:10 ` Avi Kivity [this message]
2020-02-12 10:29 ` Stefan Hajnoczi
2020-02-12 10:47 ` Paolo Bonzini
2020-02-12 10:54 ` Avi Kivity
2020-02-19 10:37 ` Stefan Hajnoczi
2020-02-19 10:43 ` Avi Kivity
2020-02-19 11:10 ` Paolo Bonzini
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