Hi, In running iozone for writes to small files, we noticed a pretty big discrepency between the performance of the deadline and cfq I/O schedulers. Investigation showed that I/O was being issued from 2 different contexts: the iozone process itself, and the jbd2/sdh-8 thread (as expected). Because of the way cfq performs slice idling, the delays introduced between the metadata and data I/Os were significant. For example, cfq would see about 7MB/s versus deadline's 35 for the same workload. I also tested fs_mark with writing and fsyncing 1000 64k files, and a similar 5x performance difference was observed. Eric Sandeen suggested that I flag the journal writes as metadata, and once I did that, the performance difference went away completely (cfq has special logic to prioritize metadata I/O). So, I'm submitting this patch for comments and testing. I have a similar patch for jbd that I will submit if folks agree that this is a good idea. Cheers, Jeff Signed-off-by: Jeff Moyer <jmoyer@xxxxxxxxxx> diff --git a/fs/jbd2/commit.c b/fs/jbd2/commit.c index 671da7f..1998265 100644 --- a/fs/jbd2/commit.c +++ b/fs/jbd2/commit.c @@ -139,7 +139,7 @@ static int journal_submit_commit_record(journal_t *journal, set_buffer_ordered(bh); barrier_done = 1; } - ret = submit_bh(WRITE_SYNC_PLUG, bh); + ret = submit_bh(WRITE_SYNC_PLUG | (1<<BIO_RW_META), bh); if (barrier_done) clear_buffer_ordered(bh); @@ -160,7 +160,7 @@ static int journal_submit_commit_record(journal_t *journal, lock_buffer(bh); set_buffer_uptodate(bh); clear_buffer_dirty(bh); - ret = submit_bh(WRITE_SYNC_PLUG, bh); + ret = submit_bh(WRITE_SYNC_PLUG | (1<<BIO_RW_META), bh); } *cbh = bh; return ret; @@ -369,7 +369,7 @@ void jbd2_journal_commit_transaction(journal_t *journal) int tag_bytes = journal_tag_bytes(journal); struct buffer_head *cbh = NULL; /* For transactional checksums */ __u32 crc32_sum = ~0; - int write_op = WRITE; + int write_op = WRITE_META; /* * First job: lock down the current transaction and wait for @@ -409,7 +409,7 @@ void jbd2_journal_commit_transaction(journal_t *journal) * instead we rely on sync_buffer() doing the unplug for us. */ if (commit_transaction->t_synchronous_commit) - write_op = WRITE_SYNC_PLUG; + write_op = WRITE_SYNC_PLUG | (1<<BIO_RW_META); trace_jbd2_commit_locking(journal, commit_transaction); stats.run.rs_wait = commit_transaction->t_max_wait; stats.run.rs_locked = jiffies; -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
