At 02:53 09/05/19, 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. > >So, are these numbers 100% reproducible? Could you capture blktrace data >for both with and without the patch, so we can take a closer look at the >generated IO for each case? Thank you for your comment. This number is 100% reproducible but the number depends on hardware environment. I will try to get blktrace data and post this. -- 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
