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Re: [Qemu-devel] [Qemu-block] [PATCH 06/10] aio-posix: remove walking_ha
From: |
Paolo Bonzini |
Subject: |
Re: [Qemu-devel] [Qemu-block] [PATCH 06/10] aio-posix: remove walking_handlers, protecting AioHandler list with list_lock |
Date: |
Wed, 30 Nov 2016 14:36:23 +0100 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.4.0 |
On 30/11/2016 14:31, Stefan Hajnoczi wrote:
> On Tue, Nov 29, 2016 at 12:47:03PM +0100, Paolo Bonzini wrote:
>> @@ -272,22 +275,32 @@ bool aio_prepare(AioContext *ctx)
>> bool aio_pending(AioContext *ctx)
>> {
>> AioHandler *node;
>> + bool result = false;
>>
>> - QLIST_FOREACH(node, &ctx->aio_handlers, node) {
>> + /*
>> + * We have to walk very carefully in case aio_set_fd_handler is
>> + * called while we're walking.
>> + */
>> + qemu_lockcnt_inc(&ctx->list_lock);
>> +
>> + QLIST_FOREACH_RCU(node, &ctx->aio_handlers, node) {
>> int revents;
>>
>> revents = node->pfd.revents & node->pfd.events;
>> if (revents & (G_IO_IN | G_IO_HUP | G_IO_ERR) && node->io_read &&
>> aio_node_check(ctx, node->is_external)) {
>> - return true;
>> + result = true;
>> + break;
>> }
>> if (revents & (G_IO_OUT | G_IO_ERR) && node->io_write &&
>> aio_node_check(ctx, node->is_external)) {
>> - return true;
>> + result = true;
>> + break;
>> }
>> }
>> + qemu_lockcnt_dec(&ctx->list_lock);
>>
>> - return false;
>> + return result;
>> }
>>
>> bool aio_dispatch(AioContext *ctx)
>> @@ -308,13 +321,12 @@ bool aio_dispatch(AioContext *ctx)
>> * We have to walk very carefully in case aio_set_fd_handler is
>> * called while we're walking.
>> */
>> - ctx->walking_handlers++;
>> + qemu_lockcnt_inc(&ctx->list_lock);
>>
>> - QLIST_FOREACH_SAFE(node, &ctx->aio_handlers, node, tmp) {
>> + QLIST_FOREACH_SAFE_RCU(node, &ctx->aio_handlers, node, tmp) {
>> int revents;
>>
>> - revents = node->pfd.revents & node->pfd.events;
>> - node->pfd.revents = 0;
>> + revents = atomic_xchg(&node->pfd.revents, 0) & node->pfd.events;
>
> Why is node->pfd.revents accessed with atomic_*() here and in aio_poll()
> but not in aio_pending()?
It could use atomic_read there, indeed.
Paolo
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- [Qemu-devel] [PATCH 03/10] aio: make ctx->list_lock a QemuLockCnt, subsuming ctx->walking_bh, (continued)
- [Qemu-devel] [PATCH 03/10] aio: make ctx->list_lock a QemuLockCnt, subsuming ctx->walking_bh, Paolo Bonzini, 2016/11/29
- [Qemu-devel] [PATCH 05/10] aio: tweak walking in dispatch phase, Paolo Bonzini, 2016/11/29
- [Qemu-devel] [PATCH 04/10] qemu-thread: optimize QemuLockCnt with futexes on Linux, Paolo Bonzini, 2016/11/29
- [Qemu-devel] [PATCH 07/10] aio-win32: remove walking_handlers, protecting AioHandler list with list_lock, Paolo Bonzini, 2016/11/29
- [Qemu-devel] [PATCH 06/10] aio-posix: remove walking_handlers, protecting AioHandler list with list_lock, Paolo Bonzini, 2016/11/29
- [Qemu-devel] [PATCH 10/10] async: optimize aio_bh_poll, Paolo Bonzini, 2016/11/29
- [Qemu-devel] [PATCH 08/10] aio: document locking, Paolo Bonzini, 2016/11/29
- [Qemu-devel] [PATCH 09/10] aio: push aio_context_acquire/release down to dispatching, Paolo Bonzini, 2016/11/29