Jan Kara <jack@xxxxxxx> writes: > 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. > This looks like a good idea to me. I'd just be careful about data=journal > mode where even data is written via journal and thus you'd incorrectly > prioritize all the IO. I suppose that could have negative impact on performace > of other filesystems on the same disk. So for data=journal mode, I'd leave > write_op to be just WRITE / WRITE_SYNC_PLUG. Hi, Jan, thanks for the review! I'm trying to figure out the best way to relay the journal mode from ext3 or ext4 to jbd or jbd2. Would a new journal flag, set in journal_init_inode, be appropriate? This wouldn't cover the case of data journalling set per inode, though. It also puts some ext3-specific code into the purportedly fs-agnostic jbd code (specifically, testing the superblock for the data journal mount flag). Do you have any suggestions? Thanks! Jeff -- 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
