David Howells <dhowells@xxxxxxxxxx> wrote: > > Have you got before/after benchmark results? > > See attached. Attached here are results using BTRFS (patched so that it'll work at all) rather than Ext3 on the client on the partition backing the cache. Note that I didn't bother redoing the tests that didn't involve a cache as the choice of filesystem backing the cache should have no bearing on the result. Generally, completely cold caches shouldn't show much variation as all the writing can be done completely asynchronously, provided the client doesn't fill its RAM. The interesting case is where the disk cache is warm, but the pagecache is cold (ie: just after a reboot after filling the caches). Here, for the two big files case, BTRFS appears quite a bit better than Ext3, showing a 21% reduction in time for the smaller case and a 13% reduction for the larger case. For the many small/medium files case, BTRFS performed significantly better (15% reduction in time) in the case where the caches were completely cold. I'm not sure why, though - perhaps because it doesn't execute a write_begin() stage during the write_one_page() call and thus doesn't go allocating disk blocks to back the data, but instead allocates them later. More surprising is that BTRFS performed significantly worse (15% increase in time) in the case where the cache on disk was fully populated and then the machine had been rebooted to clear the pagecaches. It's important to note that I've only run each test once apiece, so the numbers should be taken with a modicum of salt (bad statistics and all that). David --- =========================== FEW BIG FILES TEST ON BTRFS =========================== Completely cold caches: [root@andromeda ~]# time cat /warthog/bigfile >/dev/null real 0m2.124s user 0m0.000s sys 0m1.260s [root@andromeda ~]# time cat /warthog/biggerfile >/dev/null real 0m4.538s user 0m0.000s sys 0m2.624s Warm NFS pagecache: [root@andromeda ~]# time cat /warthog/bigfile >/dev/null real 0m0.061s user 0m0.000s sys 0m0.064s [root@andromeda ~]# time cat /warthog/biggerfile >/dev/null real 0m0.118s user 0m0.000s sys 0m0.116s Warm BTRFS pagecache, cold NFS pagecache: [root@andromeda ~]# time cat /warthog/bigfile >/dev/null real 0m0.189s user 0m0.000s sys 0m0.188s [root@andromeda ~]# time cat /warthog/biggerfile >/dev/null real 0m0.369s user 0m0.000s sys 0m0.368s Warm on-disk cache, cold pagecaches: [root@andromeda ~]# time cat /warthog/bigfile >/dev/null real 0m1.540s user 0m0.000s sys 0m1.440s [root@andromeda ~]# time cat /warthog/biggerfile >/dev/null real 0m3.132s user 0m0.000s sys 0m1.724s ============================================ MANY SMALL/MEDIUM FILE READING TEST ON BTRFS ============================================ Completely cold caches: [root@andromeda ~]# time tar cf - /warthog/aaa >/dev/zero real 0m31.838s user 0m0.192s sys 0m6.076s Warm NFS pagecache: [root@andromeda ~]# time tar cf - /warthog/aaa >/dev/zero real 0m14.841s user 0m0.148s sys 0m4.988s Warm BTRFS pagecache, cold NFS pagecache: [root@andromeda ~]# time tar cf - /warthog/aaa >/dev/zero real 0m16.773s user 0m0.148s sys 0m5.512s Warm on-disk cache, cold pagecaches: [root@andromeda ~]# time tar cf - /warthog/aaa >/dev/zero real 2m12.527s user 0m0.080s sys 0m2.908s - To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
