On Mon, Dec 5, 2016 at 8:46 AM, Chris Mason <c...@fb.com> wrote: > On 12/04/2016 04:28 PM, Chris Murphy wrote: >> >> 4.8.11-300.fc25.x86_64 >> >> I'm currently doing a btrfs send/receive and I'm seeing a rather large >> hit for crc32c, bigger than aes-ni (the volume is on dm crypt), using >> perf top. >> >> 14.03% btrfs [.] __crc32c_le >> 10.50% [kernel] [k] _aesni_enc4 >> > > This is surprising, although send/recv does do a lot of small crc runs. What > is the overall CPU usage?
Before issuing btrfs send, btrfs receive: %Cpu(s): 0.2 us, 0.2 sy, 0.0 ni, 99.5 id, 0.0 wa, 0.0 hi, 0.0 si, 0.0 st During: %Cpu(s): 5.1 us, 18.2 sy, 0.0 ni, 35.0 id, 40.2 wa, 0.7 hi, 0.8 si, 0.0 st Full output https://paste.fedoraproject.org/500097/ Lots of waiting, but most of that 18% hit is coming from the two btrfs commands themselves. The same thing doesn't happen with a btrfs scrub, which also has to compute crc's albeit just once. >Maybe pin btrfs to a single CPU and use mpstat to > see how hot that one CPU is. If we're 14% of a CPU running at 100%, that's > a big deal. If we're 14% of a CPU running at 5%, we safely ignore it. I'm not sure how to do this, but if all btrfs processes were pinned to a single core, based on the more than dozen active processes I see in top during send/receive, it would definitely soak all of that core. > >> >> Complete output is here for 1 month: >> >> https://urldefense.proofpoint.com/v2/url?u=https-3A__paste.fedoraproject.org_498914_&d=DgIBaQ&c=5VD0RTtNlTh3ycd41b3MUw&r=9QPtTAxcitoznaWRKKHoEQ&m=YXgqrDMWJP2u2reRh04tnYz4CrO5SPUhSHd1cF2OcR0&s=axoqoaw0ZkYXdDxlTODLOfzqEK7uIJHqMsBjpkyIw5o&e= >> >> I don't remember crc32's taking this much CPU before, so it seems like >> a regression but offhand I don't know when it started. >> >> [chris@f25s ~]$ dmesg | grep crc32 >> [ 4.226700] Btrfs loaded, crc32c=crc32c-intel > > > At least we know you're using the intel accelerated one. Every time someone > posts this dmesg output to the list, I owe Jeff another beer. Glad I can increase your beer liability. :-D -- Chris Murphy -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
