From 3ff2f67a7c24183fcbcfe1332e5223ac6f96438c Mon Sep 17 00:00:00 2001 From: Evgeny Yakovlev Date: Mon, 18 Jul 2016 22:39:52 +0300 Subject: block: ignore flush requests when storage is clean Some guests (win2008 server for example) do a lot of unnecessary flushing when underlying media has not changed. This adds additional overhead on host when calling fsync/fdatasync. This change introduces a write generation scheme in BlockDriverState. Current write generation is checked against last flushed generation to avoid unnessesary flushes. The problem with excessive flushing was found by a performance test which does parallel directory tree creation (from 2 processes). Results improved from 0.424 loops/sec to 0.432 loops/sec. Each loop creates 10^3 directories with 10 files in each. This affected some blkdebug testcases that were expecting error logs from failure-injected flushes which are now skipped entirely (tests 026 071 089). This also affects the performance of block jobs and thus BLOCK_JOB_READY events for driver-mirror and active block-commit commands now arrives faster, before QMP send successfully returns to caller (tests 141 144). Signed-off-by: Evgeny Yakovlev Signed-off-by: Denis V. Lunev Reviewed-by: Paolo Bonzini Message-id: 1468870792-7411-5-git-send-email-den@openvz.org CC: Kevin Wolf CC: Max Reitz CC: Stefan Hajnoczi CC: Fam Zheng CC: John Snow Signed-off-by: John Snow --- block.c | 3 +++ 1 file changed, 3 insertions(+) (limited to 'block.c') diff --git a/block.c b/block.c index 67894e0719..d2dac3dce9 100644 --- a/block.c +++ b/block.c @@ -234,6 +234,8 @@ BlockDriverState *bdrv_new(void) bs->refcnt = 1; bs->aio_context = qemu_get_aio_context(); + qemu_co_queue_init(&bs->flush_queue); + QTAILQ_INSERT_TAIL(&all_bdrv_states, bs, bs_list); return bs; @@ -2472,6 +2474,7 @@ int bdrv_truncate(BlockDriverState *bs, int64_t offset) ret = refresh_total_sectors(bs, offset >> BDRV_SECTOR_BITS); bdrv_dirty_bitmap_truncate(bs); bdrv_parent_cb_resize(bs); + ++bs->write_gen; } return ret; } -- cgit 1.4.1