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| author | John Wren Kennedy <[email protected]> | 2023-10-13 12:15:09 -0600 |
|---|---|---|
| committer | GitHub <[email protected]> | 2023-10-13 11:15:09 -0700 |
| commit | c0e58995e33479a9c1d97fb2a19f8f507cc954b7 (patch) | |
| tree | 9d135f60a4de4bee374bccc723fb7974178f481b /module | |
| parent | 380c25f6402d099310f1cf6f6d1e17e65531f958 (diff) | |
Large sync writes perform worse with slog
For synchronous write workloads with large IO sizes, a pool configured
with a slog performs worse than one with an embedded zil:
sequential_writes 1m sync ios, 16 threads
Write IOPS: 1292 438 -66.10%
Write Bandwidth: 1323570 448910 -66.08%
Write Latency: 12128400 36330970 3.0x
sequential_writes 1m sync ios, 32 threads
Write IOPS: 1293 430 -66.74%
Write Bandwidth: 1324184 441188 -66.68%
Write Latency: 24486278 74028536 3.0x
The reason is the `zil_slog_bulk` variable. In `zil_lwb_write_open`,
if a zil block is greater than 768K, the priority of the write is
downgraded from sync to async. Increasing the value allows greater
throughput. To select a value for this PR, I ran an fio workload with
the following values for `zil_slog_bulk`:
zil_slog_bulk KiB/s
1048576 422132
2097152 478935
4194304 533645
8388608 623031
12582912 827158
16777216 1038359
25165824 1142210
33554432 1211472
50331648 1292847
67108864 1308506
100663296 1306821
134217728 1304998
At 64M, the results with a slog are now improved to parity with an
embedded zil:
sequential_writes 1m sync ios, 16 threads
Write IOPS: 438 1288 2.9x
Write Bandwidth: 448910 1319062 2.9x
Write Latency: 36330970 12163408 -66.52%
sequential_writes 1m sync ios, 32 threads
Write IOPS: 430 1290 3.0x
Write Bandwidth: 441188 1321693 3.0x
Write Latency: 74028536 24519698 -66.88%
None of the other tests in the performance suite (run with a zil or
slog) had a significant change, including the random_write_zil tests,
which use multiple datasets.
Reviewed-by: Alexander Motin <[email protected]>
Reviewed-by: Tony Nguyen <[email protected]>
Signed-off-by: John Wren Kennedy <[email protected]>
Closes #14378
Diffstat (limited to 'module')
| -rw-r--r-- | module/zfs/zil.c | 2 |
1 files changed, 1 insertions, 1 deletions
diff --git a/module/zfs/zil.c b/module/zfs/zil.c index 18c6cbf02..a11886136 100644 --- a/module/zfs/zil.c +++ b/module/zfs/zil.c @@ -145,7 +145,7 @@ static int zil_nocacheflush = 0; * Any writes above that will be executed with lower (asynchronous) priority * to limit potential SLOG device abuse by single active ZIL writer. */ -static uint64_t zil_slog_bulk = 768 * 1024; +static uint64_t zil_slog_bulk = 64 * 1024 * 1024; static kmem_cache_t *zil_lwb_cache; static kmem_cache_t *zil_zcw_cache; |