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[PATCH v4] linux-aio: add IO_CMD_FDSYNC command support

Prasad Pandit posted 1 patch 1 month, 2 weeks ago
Patches applied successfully (tree, apply log)
git fetch https://github.com/patchew-project/qemu tags/patchew/20240314111628.1508636-1-ppandit@redhat.com
Maintainers: Kevin Wolf <kwolf@redhat.com>, Hanna Reitz <hreitz@redhat.com>
There is a newer version of this series
block/file-posix.c      |  7 +++++++
block/linux-aio.c       | 21 ++++++++++++++++++++-
include/block/raw-aio.h |  1 +
3 files changed, 28 insertions(+), 1 deletion(-)
[PATCH v4] linux-aio: add IO_CMD_FDSYNC command support
Posted by Prasad Pandit 1 month, 2 weeks ago 
From: Prasad Pandit <pjp@fedoraproject.org>

Libaio defines IO_CMD_FDSYNC command to sync all outstanding
asynchronous I/O operations, by flushing out file data to the
disk storage.

Enable linux-aio to submit such aio request. This helps to
reduce latency induced via pthread_create calls by
thread-pool (aio=threads).

Signed-off-by: Prasad Pandit <pjp@fedoraproject.org>
---
 block/file-posix.c      |  7 +++++++
 block/linux-aio.c       | 21 ++++++++++++++++++++-
 include/block/raw-aio.h |  1 +
 3 files changed, 28 insertions(+), 1 deletion(-)

v4: New boolean field to indicate if aio_fdsync is available or not.
    It is set at file open time and checked before AIO_FLUSH call.
  - https://lists.nongnu.org/archive/html/qemu-devel/2024-03/msg03701.html

diff --git a/block/file-posix.c b/block/file-posix.c
index 35684f7e21..78a8cea03b 100644
--- a/block/file-posix.c
+++ b/block/file-posix.c
@@ -159,6 +159,7 @@ typedef struct BDRVRawState {
     bool has_discard:1;
     bool has_write_zeroes:1;
     bool use_linux_aio:1;
+    bool has_laio_fdsync:1;
     bool use_linux_io_uring:1;
     int page_cache_inconsistent; /* errno from fdatasync failure */
     bool has_fallocate;
@@ -718,6 +719,7 @@ static int raw_open_common(BlockDriverState *bs, QDict *options,
         ret = -EINVAL;
         goto fail;
     }
+    s->has_laio_fdsync = laio_has_fdsync(s->fd);
 #else
     if (s->use_linux_aio) {
         error_setg(errp, "aio=native was specified, but is not supported "
@@ -2599,6 +2601,11 @@ static int coroutine_fn raw_co_flush_to_disk(BlockDriverState *bs)
     if (raw_check_linux_io_uring(s)) {
         return luring_co_submit(bs, s->fd, 0, NULL, QEMU_AIO_FLUSH);
     }
+#endif
+#ifdef CONFIG_LINUX_AIO
+    if (s->has_laio_fdsync && raw_check_linux_aio(s)) {
+        return laio_co_submit(s->fd, 0, NULL, QEMU_AIO_FLUSH, 0);
+    }
 #endif
     return raw_thread_pool_submit(handle_aiocb_flush, &acb);
 }
diff --git a/block/linux-aio.c b/block/linux-aio.c
index ec05d946f3..e3b5ec9aba 100644
--- a/block/linux-aio.c
+++ b/block/linux-aio.c
@@ -384,6 +384,9 @@ static int laio_do_submit(int fd, struct qemu_laiocb *laiocb, off_t offset,
     case QEMU_AIO_READ:
         io_prep_preadv(iocbs, fd, qiov->iov, qiov->niov, offset);
         break;
+    case QEMU_AIO_FLUSH:
+        io_prep_fdsync(iocbs, fd);
+        break;
     /* Currently Linux kernel does not support other operations */
     default:
         fprintf(stderr, "%s: invalid AIO request type 0x%x.\n",
@@ -412,7 +415,7 @@ int coroutine_fn laio_co_submit(int fd, uint64_t offset, QEMUIOVector *qiov,
     AioContext *ctx = qemu_get_current_aio_context();
     struct qemu_laiocb laiocb = {
         .co         = qemu_coroutine_self(),
-        .nbytes     = qiov->size,
+        .nbytes     = qiov ? qiov->size : 0,
         .ctx        = aio_get_linux_aio(ctx),
         .ret        = -EINPROGRESS,
         .is_read    = (type == QEMU_AIO_READ),
@@ -486,3 +489,19 @@ void laio_cleanup(LinuxAioState *s)
     }
     g_free(s);
 }
+
+bool laio_has_fdsync(int fd)
+{
+    struct iocb cb;
+    struct iocb *cbs[] = {&cb, NULL};
+
+    io_context_t ctx = 0;
+    io_setup(1, &ctx);
+
+    /* check if host kernel supports IO_CMD_FDSYNC */
+    io_prep_fdsync(&cb, fd);
+    int ret = io_submit(ctx, 1, cbs);
+
+    io_destroy(ctx);
+    return (ret == -EINVAL) ? false : true;
+}
diff --git a/include/block/raw-aio.h b/include/block/raw-aio.h
index 20e000b8ef..626706827f 100644
--- a/include/block/raw-aio.h
+++ b/include/block/raw-aio.h
@@ -60,6 +60,7 @@ void laio_cleanup(LinuxAioState *s);
 int coroutine_fn laio_co_submit(int fd, uint64_t offset, QEMUIOVector *qiov,
                                 int type, uint64_t dev_max_batch);
 
+bool laio_has_fdsync(int);
 void laio_detach_aio_context(LinuxAioState *s, AioContext *old_context);
 void laio_attach_aio_context(LinuxAioState *s, AioContext *new_context);
 #endif
-- 
2.44.0
Re: [PATCH v4] linux-aio: add IO_CMD_FDSYNC command support
Posted by Kevin Wolf 3 days, 9 hours ago 
Am 14.03.2024 um 12:16 hat Prasad Pandit geschrieben:
> From: Prasad Pandit <pjp@fedoraproject.org>
> 
> Libaio defines IO_CMD_FDSYNC command to sync all outstanding
> asynchronous I/O operations, by flushing out file data to the
> disk storage.
> 
> Enable linux-aio to submit such aio request. This helps to
> reduce latency induced via pthread_create calls by
> thread-pool (aio=threads).
> 
> Signed-off-by: Prasad Pandit <pjp@fedoraproject.org>

As we discussed in chat, it would be good to be more detailed about the
scenario that we're really concerned about here. The commit message
above sounds like submitting fdsync takes too long, but the real concern
seems to be about the effect that creating and destroying a thread has
on a vcpu by adding a TLB flush. Describing the mechanisms, the sequence
of operations that happen and the problem this causes in more detail
would make the commit message a lot more useful.

>  block/file-posix.c      |  7 +++++++
>  block/linux-aio.c       | 21 ++++++++++++++++++++-
>  include/block/raw-aio.h |  1 +
>  3 files changed, 28 insertions(+), 1 deletion(-)
> 
> v4: New boolean field to indicate if aio_fdsync is available or not.
>     It is set at file open time and checked before AIO_FLUSH call.
>   - https://lists.nongnu.org/archive/html/qemu-devel/2024-03/msg03701.html
> 
> diff --git a/block/file-posix.c b/block/file-posix.c
> index 35684f7e21..78a8cea03b 100644
> --- a/block/file-posix.c
> +++ b/block/file-posix.c
> @@ -159,6 +159,7 @@ typedef struct BDRVRawState {
>      bool has_discard:1;
>      bool has_write_zeroes:1;
>      bool use_linux_aio:1;
> +    bool has_laio_fdsync:1;
>      bool use_linux_io_uring:1;
>      int page_cache_inconsistent; /* errno from fdatasync failure */
>      bool has_fallocate;
> @@ -718,6 +719,7 @@ static int raw_open_common(BlockDriverState *bs, QDict *options,
>          ret = -EINVAL;
>          goto fail;
>      }
> +    s->has_laio_fdsync = laio_has_fdsync(s->fd);

I think this should be conditional on s->use_linux_aio. No point in
probing it if we'll never call it anyway.

Kevin
Re: [PATCH v4] linux-aio: add IO_CMD_FDSYNC command support
Posted by Stefan Hajnoczi 1 month, 2 weeks ago 
On Thu, Mar 14, 2024 at 04:46:28PM +0530, Prasad Pandit wrote:
> From: Prasad Pandit <pjp@fedoraproject.org>
> 
> Libaio defines IO_CMD_FDSYNC command to sync all outstanding
> asynchronous I/O operations, by flushing out file data to the
> disk storage.
> 
> Enable linux-aio to submit such aio request. This helps to
> reduce latency induced via pthread_create calls by
> thread-pool (aio=threads).
> 
> Signed-off-by: Prasad Pandit <pjp@fedoraproject.org>
> ---
>  block/file-posix.c      |  7 +++++++
>  block/linux-aio.c       | 21 ++++++++++++++++++++-
>  include/block/raw-aio.h |  1 +
>  3 files changed, 28 insertions(+), 1 deletion(-)
> 
> v4: New boolean field to indicate if aio_fdsync is available or not.
>     It is set at file open time and checked before AIO_FLUSH call.
>   - https://lists.nongnu.org/archive/html/qemu-devel/2024-03/msg03701.html

Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>

Patchew 2.1-devel-0870f84

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