At 11:51 09/05/20, Wu Fengguang wrote: >On Mon, May 18, 2009 at 07:53:00PM +0200, Jens Axboe wrote: >> On Mon, May 18 2009, Hisashi Hifumi wrote: >> > Hi. >> > >> > I wrote a patch that adds blk_run_backing_dev on page_cache_async_readahead >> > so readahead I/O is unpluged to improve throughput. >> > >> > Following is the test result with dd. >> > >> > #dd if=testdir/testfile of=/dev/null bs=16384 >> > >> > -2.6.30-rc6 >> > 1048576+0 records in >> > 1048576+0 records out >> > 17179869184 bytes (17 GB) copied, 224.182 seconds, 76.6 MB/s >> > >> > -2.6.30-rc6-patched >> > 1048576+0 records in >> > 1048576+0 records out >> > 17179869184 bytes (17 GB) copied, 206.465 seconds, 83.2 MB/s >> > >> > Sequential read performance on a big file was improved. >> > Please merge my patch. >> > >> > Thanks. >> > >> > Signed-off-by: Hisashi Hifumi <hifumi.hisashi@xxxxxxxxxxxxx> >> > >> > diff -Nrup linux-2.6.30-rc6.org/mm/readahead.c >linux-2.6.30-rc6.unplug/mm/readahead.c >> > --- linux-2.6.30-rc6.org/mm/readahead.c 2009-05-18 10:46:15.000000000 +0900 >> > +++ linux-2.6.30-rc6.unplug/mm/readahead.c 2009-05-18 >13:00:42.000000000 +0900 >> > @@ -490,5 +490,7 @@ page_cache_async_readahead(struct addres >> > >> > /* do read-ahead */ >> > ondemand_readahead(mapping, ra, filp, true, offset, req_size); >> > + >> > + blk_run_backing_dev(mapping->backing_dev_info, NULL); >> > } >> > EXPORT_SYMBOL_GPL(page_cache_async_readahead); >> >> I'm surprised this makes much of a difference. It seems correct to me to >> NOT unplug the device, since it will get unplugged when someone ends up >> actually waiting for a page. And that will then kick off the remaining >> IO as well. For this dd case, you'll be hitting lock_page() for the >> readahead page really soon, definitely not long enough to warrant such a >> big difference in speed. > >The possible timing change of this patch is (assuming readahead size=100): > >T0 read(100), which triggers readahead(200, 100) >T1 read(101) >T2 read(102) >... >T100 read(200), find_get_page(200) => readahead(300, 100) > lock_page(200) => implicit unplug > >The readahead(200, 100) submitted at time T0 *might* be delayed to the >unplug time of T100. > >But that is only a possibility. In normal cases, the read(200) would >be blocking and there will be a lock_page(200) that will immediately >unplug device for readahead(300, 100). Hi Andrew. Following patch improves sequential read performance and does not harm other performance. Please merge my patch. Comments? Thanks. #dd if=testdir/testfile of=/dev/null bs=16384 -2.6.30-rc6 1048576+0 records in 1048576+0 records out 17179869184 bytes (17 GB) copied, 224.182 seconds, 76.6 MB/s -2.6.30-rc6-patched 1048576+0 records in 1048576+0 records out 17179869184 bytes (17 GB) copied, 206.465 seconds, 83.2 MB/s Signed-off-by: Hisashi Hifumi <hifumi.hisashi@xxxxxxxxxxxxx> diff -Nrup linux-2.6.30-rc6.org/mm/readahead.c linux-2.6.30-rc6.unplug/mm/readahead.c --- linux-2.6.30-rc6.org/mm/readahead.c 2009-05-18 10:46:15.000000000 +0900 +++ linux-2.6.30-rc6.unplug/mm/readahead.c 2009-05-18 13:00:42.000000000 +0900 @@ -490,5 +490,7 @@ page_cache_async_readahead(struct addres /* do read-ahead */ ondemand_readahead(mapping, ra, filp, true, offset, req_size); + + blk_run_backing_dev(mapping->backing_dev_info, NULL); } EXPORT_SYMBOL_GPL(page_cache_async_readahead); -- 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
