Excerpts from Andrew Lutomirski's message of 2011-02-11 10:08:52 -0500: > As I type this, I have an ssh process running that's dumping data into > a fifo at high speed (maybe 500Mbps) and a tar process that's > untarring from the same fifo onto btrfs. The btrfs fs is mounted -o > space_cache,compress. This machine has 8GB ram, 8 logical cores, and > a fast (i7-2600) CPU, so it's not an issue with the machine struggling > under load. > > Every few tens of seconds, my system stalls for several seconds. > These stalls cause keyboard input to be lost, firefox to hang, etc. > > Setting tar's ionice priority to best effort / 7 or to idle makes no > difference. > > ionice idle and queue_depth = 1 on the disk (a slow 2TB WD) also makes > no difference. > > max_sectors_kb = 64 in addition to the above doesn't help either. > > latencytop shows regular instances of 2-7 *second* latency, variously > in sync_page, start_transaction, btrfs_start_ordered_extent, and > do_get_write_access (from jbd2 on my ext4 root partition). > > echo 3 >drop_caches gave me 7 GB free RAM. I still had stalls when > 4-5 GB were still free (so it shouldn't be a problem with important > pages being evicted). > > In case it matters, all of my partitions are on LVM on dm-crypt, but > this machine has AES-NI so the overhead from that should be minimal. > In fact, overall CPU usage is only about 10%. > > What gives? I thought this stuff was supposed to be better on modern kernels.
We can tell more if you post the full traces from latencytop. I have a patch here for latencytop that adds a -c mode, which dumps the traces out to a text files. http://oss.oracle.com/~mason/latencytop.patch Based on what you have here, I think it's probably a latency problem between btrfs and the dm-crypt stuff. How easily can setup a test partition without dm-crypt? -chris -- 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