That's strange-- are you doing the same test scenario? How much random I/O did you ask for? My tests took 6-7 minutes to do the 30G of 8k not-repeating I/Os in a 30G file (about 9k IOPs for me-- it's actually significantly faster but then starves every few seconds-- not new with these patches).. your cache device if 3.8T, so to have a similar 12-13% of the cache you'd need to do 15x as much (90 mins if you're the same speed--- but your I/O subsystem is also much faster...) If you're doing more like 3.8T of writes-- note that's not the same test. (It will result in less contiguous stuff in the cache and it will be less repeatable / more volatile). Mike On Sat, Sep 30, 2017 at 9:51 PM, Coly Li <i@xxxxxxx> wrote: > On 2017/10/1 上午6:49, Michael Lyle wrote: >> One final attempt to resend, because gmail has been giving me trouble >> sending plain text mail. >> >> Two instances of this. Tested as above, with a big set of random I/Os >> that ultimately cover every block in a file (e.g. allowing sequential >> writeback). >> >> With the 5 patches, samsung 940 SSD cache + crummy 5400 RPM USB hard drive: >> >> Typical seconds look like: >> >> Reading 38232K from cache in 4809 IO. 38232/4809=7.95k per cache device IO. >> >> Writing 38112k to cache in 400 I/O = 95.28k -- or we are combining >> about 11.9 extents to a contiguous writeback. Tracing, there are >> still contiguous things that are not getting merged well, but it's OK. >> (I'm hoping plugging makes this better). >> >> sda 4809.00 38232.00 446.00 38232 446 >> sdb 400.00 0.00 38112.00 0 38112 >> >> Without the 5 patches, a typical second-- >> >> sda 2509.00 19968.00 316.00 19968 316 >> sdb 502.00 0.00 19648.00 0 38112 >> >> or we are combining about 4.9 extents to a contiguous writeback, and >> writing back at about half the rate. All of these numbers are +/- 10% >> and obtained by eyeballing and grabbing representative seconds. >> >> Mike >> >> On Sat, Sep 30, 2017 at 2:02 AM, Michael Lyle <mlyle@xxxxxxxx> wrote: >>> >>> Resent because I can't seem to get gmail to not send HTML mail. And off to sleep. >>> >>> >>> On Sat, Sep 30, 2017 at 1:57 AM, Michael Lyle <mlyle@xxxxxxxx> wrote: >>>> Two instances of this. >>>> >>>> With the 5 patches, samsung 940 SSD cache + crummy 5400 RPM USB hard drive: >>>> >>>> Typical seconds look like: >>>> >>>> Reading 38232K from cache in 4809 IO. 38232/4809=7.95k per cache device IO. >>>> >>>> Writing 38112k to cache in 400 I/O = 95.28k -- or we are combining about >>>> 11.9 extents to a contiguous writeback. Tracing, there are still contiguous >>>> things that are not getting merged well, but it's OK. (I'm hoping plugging >>>> makes this better). >>>> >>>> sda 4809.00 38232.00 446.00 38232 446 >>>> sdb 400.00 0.00 38112.00 0 38112 >>>> >>>> Without the 5 patches, a typical second-- >>>> >>>> sda 2509.00 19968.00 316.00 19968 316 >>>> sdb 502.00 0.00 19648.00 0 38112 >>>> >>>> or we are combining about 4.9 extents to a contiguous writeback, and writing >>>> back at about half the rate. > > Hi Mike, > > Get it. Now I am testing your patches (all 5 patches). It has been 12+ > hours, should be 12+ hours more. The backing device is a raid0 composed > by 4x1.8T 2.5inch harddisk, cache device is a 3.8T NVMe SSD. Block size > is 512K. > > Hope it works as you expected on my server. > > -- > Coly Li -- 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
