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
