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From: Paolo Bonzini <pbonzini@redhat.com>
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Date: Tue, 7 Jul 2015 17:27:16 +0200
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Subject: Re: [Qemu-devel] [PATCH RFC 4/4] aio-posix: Use epoll in aio_poll
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To: Stefan Hajnoczi <stefanha@redhat.com>, Fam Zheng <famz@redhat.com>
Cc: Kevin Wolf <kwolf@redhat.com>, qemu-devel@nongnu.org, qemu-block@nongnu.org



On 07/07/2015 17:08, Stefan Hajnoczi wrote:
>> > +
>> > +#define EPOLL_BATCH 128
>> > +static bool aio_poll_epoll(AioContext *ctx, bool blocking)
>> > +{
>> > +    AioHandler *node;
>> > +    bool was_dispatching;
>> > +    int i, ret;
>> > +    bool progress;
>> > +    int64_t timeout;
>> > +    struct epoll_event events[EPOLL_BATCH];
>> > +
>> > +    aio_context_acquire(ctx);
>> > +    was_dispatching = ctx->dispatching;
>> > +    progress = false;
>> > +
>> > +    /* aio_notify can avoid the expensive event_notifier_set if
>> > +     * everything (file descriptors, bottom halves, timers) will
>> > +     * be re-evaluated before the next blocking poll().  This is
>> > +     * already true when aio_poll is called with blocking == false;
>> > +     * if blocking == true, it is only true after poll() returns.
>> > +     *
>> > +     * If we're in a nested event loop, ctx->dispatching might be true.
>> > +     * In that case we can restore it just before returning, but we
>> > +     * have to clear it now.
>> > +     */
>> > +    aio_set_dispatching(ctx, !blocking);
>> > +
>> > +    ctx->walking_handlers++;
>> > +
>> > +    timeout = blocking ? aio_compute_timeout(ctx) : 0;
>> > +
>> > +    if (timeout > 0) {
>> > +        timeout = DIV_ROUND_UP(timeout, 1000000);
>> > +    }
> I think you already posted the timerfd code in an earlier series.  Why
> degrade to millisecond precision?  It needs to be fixed up anyway if the
> main loop uses aio_poll() in the future.

BTW, what about putting the code in a separate aio-epoll.c file?

Paolo