tools/virtiofsd/fuse_virtio.c | 1 + 1 file changed, 1 insertion(+)
With the thread pool disabled, we add the requests in the queue to a
GList, processing by iterating over there afterwards.
For adding them, we're using "g_list_prepend()", which is more
efficient but causes the requests to be processed in reverse order,
breaking the read-ahead and request-merging optimizations in the host
for sequential operations.
According to the documentation, if you need to process the request
in-order, using "g_list_prepend()" and then reversing the list with
"g_list_reverse()" is more efficient than using "g_list_append()", so
let's do it that way.
Testing on a spinning disk (to boost the increase of read-ahead and
request-merging) shows a 4x improvement on sequential write fio test:
Test:
fio --directory=/mnt/virtio-fs --filename=fio-file1 --runtime=20
--iodepth=16 --size=4G --direct=1 --blocksize=4K --ioengine libaio
--rw write --name seqwrite-libaio
Without "g_list_reverse()":
...
Jobs: 1 (f=1): [W(1)][100.0%][w=22.4MiB/s][w=5735 IOPS][eta 00m:00s]
seqwrite-libaio: (groupid=0, jobs=1): err= 0: pid=710: Tue Aug 24 12:58:16 2021
write: IOPS=5709, BW=22.3MiB/s (23.4MB/s)(446MiB/20002msec); 0 zone resets
...
With "g_list_reverse()":
...
Jobs: 1 (f=1): [W(1)][100.0%][w=84.0MiB/s][w=21.5k IOPS][eta 00m:00s]
seqwrite-libaio: (groupid=0, jobs=1): err= 0: pid=716: Tue Aug 24 13:00:15 2021
write: IOPS=21.3k, BW=83.1MiB/s (87.2MB/s)(1663MiB/20001msec); 0 zone resets
...
Signed-off-by: Sergio Lopez <slp@redhat.com>
---
tools/virtiofsd/fuse_virtio.c | 1 +
1 file changed, 1 insertion(+)
diff --git a/tools/virtiofsd/fuse_virtio.c b/tools/virtiofsd/fuse_virtio.c
index fc2564a603..8f4fd165b9 100644
--- a/tools/virtiofsd/fuse_virtio.c
+++ b/tools/virtiofsd/fuse_virtio.c
@@ -716,6 +716,7 @@ static void *fv_queue_thread(void *opaque)
/* Process all the requests. */
if (!se->thread_pool_size && req_list != NULL) {
+ req_list = g_list_reverse(req_list);
g_list_foreach(req_list, fv_queue_worker, qi);
g_list_free(req_list);
req_list = NULL;
--
2.26.2
On Tue, Aug 24, 2021 at 03:11:58PM +0200, Sergio Lopez wrote: > With the thread pool disabled, we add the requests in the queue to a > GList, processing by iterating over there afterwards. > > For adding them, we're using "g_list_prepend()", which is more > efficient but causes the requests to be processed in reverse order, > breaking the read-ahead and request-merging optimizations in the host > for sequential operations. > > According to the documentation, if you need to process the request > in-order, using "g_list_prepend()" and then reversing the list with > "g_list_reverse()" is more efficient than using "g_list_append()", so > let's do it that way. > > Testing on a spinning disk (to boost the increase of read-ahead and > request-merging) shows a 4x improvement on sequential write fio test: > > Test: > fio --directory=/mnt/virtio-fs --filename=fio-file1 --runtime=20 > --iodepth=16 --size=4G --direct=1 --blocksize=4K --ioengine libaio > --rw write --name seqwrite-libaio > > Without "g_list_reverse()": > ... > Jobs: 1 (f=1): [W(1)][100.0%][w=22.4MiB/s][w=5735 IOPS][eta 00m:00s] > seqwrite-libaio: (groupid=0, jobs=1): err= 0: pid=710: Tue Aug 24 12:58:16 2021 > write: IOPS=5709, BW=22.3MiB/s (23.4MB/s)(446MiB/20002msec); 0 zone resets > ... > > With "g_list_reverse()": > ... > Jobs: 1 (f=1): [W(1)][100.0%][w=84.0MiB/s][w=21.5k IOPS][eta 00m:00s] > seqwrite-libaio: (groupid=0, jobs=1): err= 0: pid=716: Tue Aug 24 13:00:15 2021 > write: IOPS=21.3k, BW=83.1MiB/s (87.2MB/s)(1663MiB/20001msec); 0 zone resets > ... > That's a very impressive improvememnt. Thanks Sergio for fixing this. Reviewed-by: Vivek Goyal <vgoyal@redhat.com> Vivek > Signed-off-by: Sergio Lopez <slp@redhat.com> > --- > tools/virtiofsd/fuse_virtio.c | 1 + > 1 file changed, 1 insertion(+) > > diff --git a/tools/virtiofsd/fuse_virtio.c b/tools/virtiofsd/fuse_virtio.c > index fc2564a603..8f4fd165b9 100644 > --- a/tools/virtiofsd/fuse_virtio.c > +++ b/tools/virtiofsd/fuse_virtio.c > @@ -716,6 +716,7 @@ static void *fv_queue_thread(void *opaque) > > /* Process all the requests. */ > if (!se->thread_pool_size && req_list != NULL) { > + req_list = g_list_reverse(req_list); > g_list_foreach(req_list, fv_queue_worker, qi); > g_list_free(req_list); > req_list = NULL; > -- > 2.26.2 >
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