On Tue, Jun 30, 2015 at 09:19:45PM +0800, Fam Zheng wrote: > ===================================================================== > # of scsi-disks | master | epoll > | rd wr randrw | rd wr randrw > --------------------------------------------------------------------- > 1 | 103 96 49 | 105 99 49 > 4 | 92 96 48 | 103 98 49 > 8 | 96 94 46 | 101 97 50 > 16 | 91 91 45 | 101 95 48 > 32 | 84 83 40 | 95 95 48 > 64 | 75 73 35 | 91 90 44 > 128 | 54 53 26 | 79 80 39 > 256 | 41 39 19 | 63 62 30 > =====================================================================
Nice results!
> @@ -44,6 +47,12 @@ static AioHandler *find_aio_handler(AioContext *ctx, int
> fd)
>
> void aio_context_setup(AioContext *ctx, Error **errp)
> {
> +#ifdef CONFIG_EPOLL
> + ctx->epollfd = epoll_create1(EPOLL_CLOEXEC);
> + if (ctx->epollfd < 0) {
> + error_setg(errp, "Failed to create epoll fd: %s", strerror(errno));
Slightly more concise:
error_setg_errno(errp, errno, "Failed to create epoll fd")
> -/* These thread-local variables are used only in a small part of aio_poll
> +#ifdef CONFIG_EPOLL
> +QEMU_BUILD_BUG_ON((int)G_IO_IN != EPOLLIN);
> +QEMU_BUILD_BUG_ON((int)G_IO_OUT != EPOLLOUT);
> +QEMU_BUILD_BUG_ON((int)G_IO_PRI != EPOLLPRI);
> +QEMU_BUILD_BUG_ON((int)G_IO_ERR != EPOLLERR);
> +QEMU_BUILD_BUG_ON((int)G_IO_HUP != EPOLLHUP);
I guess this assumption is okay but maybe the compiler optimizes:
event.events = (node->pfd.events & G_IO_IN ? EPOLLIN : 0) |
(node->pfd.events & G_IO_OUT ? EPOLLOUT : 0) |
(node->pfd.events & G_IO_PRI ? EPOLLPRI : 0) |
(node->pfd.events & G_IO_ERR ? EPOLLERR : 0) |
(node->pfd.events & G_IO_HUP ? EPOLLHUP : 0);
into:
events.events = node->pfd.events & (EPOLLIN | EPOLLOUT | EPOLLPRI |
EPOLLERR | EPOLLHUP);
which is just an AND instruction so it's effectively free and doesn't
assume that these constants have the same values.
> +
> +#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.
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