On Mon, 2 May 2011, Jens Axboe wrote: > On 2011-05-02 08:17, Lukas Czerner wrote: > > 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. > > Good results. It'd be more efficient to add the vectored discard support > and use it for this too though, and it would get rid of the need to wait > on the batches since there'd be just one discard bio for the ranges. > Since we do not have vectored discard yet, can this change go in as it is ? Also, Christoph thinks that it would not help anyway since the we do batch the discard requests only when it exceeds the max range. Thanks! -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
