On Thu, 28 Apr 2011, Lukas Czerner wrote: > On Wed, 27 Apr 2011, Jeff Moyer wrote: > > > Lukas Czerner <lczerner@xxxxxxxxxx> writes: > > > > > Currently we are waiting for every submitted REQ_DISCARD bio separately, > > > but it can have unwanted consequences of repeatedly flushing the queue, > > > so we rather submit bios in batches and wait for the entire batch, hence > > > narrowing the window of other ios going in. > > > > > > Use bio_batch_end_io() and struct bio_batch for that purpose, the same > > > is used by blkdev_issue_zeroout(). Also change bio_batch_end_io() so we > > > always set !BIO_UPTODATE in the case of error and remove the check for > > > bb, since we are the only user of this function and we always set this. > > > > > > Remove bio_get()/bio_put() from the blkdev_issue_discard() since > > > bio_alloc() and bio_batch_end_io() is doing the same thing, hence it is > > > not needed anymore. > > > > > > I have done simple dd testing with surprising results. The script I have > > > used is: > > > > > > for i in $(seq 10); do > > > echo $i > > > dd if=/dev/sdb1 of=/dev/sdc1 bs=4k & > > > sleep 5 > > > done > > > /usr/bin/time -f %e ./blkdiscard /dev/sdc1 > > > > > > Running time of BLKDISCARD on the whole device: > > > with patch without patch > > > 0.95 15.58 > > > > > > So we can see that in this artificial test the kernel with the patch > > > applied is approx 16x faster in discarding the device. > > > > I don't see any major problems here. I would like you to test > > explicitly for queue_flag_discard before submitting any bios, though. Btw, this is already in there: if (!blk_queue_discard(q)) return -EOPNOTSUPP; at the top of the function. > > Previously, after the first bio returned EOPNOTSUPP, you errored out. > > Now, you submit all bios that will end with the same failure. It's > > definitely suboptimal, and you already have the q, so you might as well > > test for this early on. > > > > Also, as I noted to you on irc, another fix required in this area is > > submitting discard requests (the final one in the batch) that do not > > honor the discard granularity exported by the device. That's not > > directly related to this patch, though. > > > > Cheers, > > Jeff > > > > Thanks for review and comments Jeff, I'll resend patches after I retest > them. > > -Lukas > -- -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
