Hi Kent, thank you for your answer. I did not re-stated it, but I am in writeback mode. I did the command you quoted, and the following commands are supposed to tell me that it was correctly taken into account (and give additional details): # cat /sys/block/bcache0/bcache/cache_mode writethrough [writeback] writearound none # cat /sys/block/bcache0/bcache/writeback_running 1 # cat /sys/block/bcache0/bcache/writeback_percent 10 I just tried to reset the cache_mode value (to writeback), it did not change anything significant. Please tell me what data I can provide, debugging information or whatever. I am still using the bcache-for-upstream branch. Leslie. On Wed, May 1, 2013 at 8:56 PM, Kent Overstreet <koverstreet@xxxxxxxxxx> wrote: > On Wed, May 01, 2013 at 06:56:41PM +0200, Leslie Basmid wrote: >> Hi Matthew, >> >> this is a very good question to start with. I am in fact very >> surprised by two things: >> >> 1. The results I have on a cached filesystem are not that far away >> from those I am getting from a not-cached FS; > >> 2. The results I am getting as write performance seems very far from >> those that are exposed for a similar benchmark >> on bcache front page (accounting for tens of thousand IOPS). > > Your read numbers are much better than any rotating disk will give > you - and as for the write numbers, you're still in writethrough mode. > The docs have the command you want: > > # echo writeback > cache_mode > >> I understand that my benchmark is done on a cached partition set up as >> a LVM, and on a file laid out on a XFS formatted VG. This must have a >> cost, but this huge ? >> I also understand that the SSD on my laptop may have poorer >> performances than the one used by Kent for his benchmark, yet the >> difference is huge (18.5K >> 454). Hence my eyebrows rising... >> >> Cheers, >> Leslie. >> >> On Wed, May 1, 2013 at 5:36 PM, matthew patton <pattonme@xxxxxxxxx> wrote: >> >> I am obtaining the following figures, on a cached fs: >> >> seq-read: iops=12188 >> >> rand-read: iops=7392 >> >> seq-write: iops=430 >> >> rand-write: iops=454 >> > >> > Just what numbers were you expecting to see? A decent 7200RPM drive can only muster 70 IOPs on a good day. The lies the SSD vendors print in their literature and on the side of the box are almost always done with a blocksize of 512 bytes. So if you're doing 4K operations, divide by 8 at least. >> -- >> To unsubscribe from this list: send the line "unsubscribe linux-bcache" in >> the body of a message to majordomo@xxxxxxxxxxxxxxx >> More majordomo info at http://vger.kernel.org/majordomo-info.html -- To unsubscribe from this list: send the line "unsubscribe linux-bcache" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
