Re: [performance bug] kernel building regression on 64 LCPUsmachine

From: Shaohua Li
Date: Tue Jan 18 2011 - 21:03:57 EST


add Jan and Theodore to the loop.

On Wed, 2011-01-19 at 09:55 +0800, Shi, Alex wrote:
> Shaohua and I tested kernel building performance on latest kernel. and
> found it is drop about 15% on our 64 LCPUs NHM-EX machine on ext4 file
> system. We find this performance dropping is due to commit
> 749ef9f8423054e326f. If we revert this patch or just change the
> WRITE_SYNC back to WRITE in jbd2/commit.c file. the performance can be
> recovered.
>
> iostat report show with the commit, read request merge number increased
> and write request merge dropped. The total request size increased and
> queue length dropped. So we tested another patch: only change WRITE_SYNC
> to WRITE_SYNC_PLUG in jbd2/commit.c, but nothing effected.
since WRITE_SYNC_PLUG doesn't work, this isn't a simple no-write-merge issue.

> we didn't test deadline IO mode, just test cfq. seems insert write
> request into sync queue effect much read performance, but we don't know
> details. What's your comments of this?
>
> iostat of .37 kernel:
> rrqm/s wrqm/s r/s w/s rMB/s wMB/s avgrq-sz avgqu-sz await svctm %util
> 22.5772 96.46 92.3742 14.747 1.0048 0.439474 34.8557 0.18078 3.8076 0.30447 2.94302
> iostat of commit reverted .37:
> 26.6223 80.21 107.875 6.03538 1.51415 0 41.3275 0.153385 3.80569 0.377231 3.22323
>
> vmstat report show, read bandwidth dropping:
> vmstat of .37:
> r b swpd free buff cache si so bi bo in cs us sy id wa st
> 3.4 52.6 0.0 64303937.0 16466.7 121544.5 0.0 0.0 2102.7 1914.6 7414.1 3185.7 2.0 1.0 80.3 16.7 0.0
> vmstat of revert all from .37
> 2.2 35.8 0.0 64306767.4 17265.6 126101.2 0.0 0.0 2415.8 1619.1 8532.2 3556.2 2.5 1.1 83.0 13.3 0.0
>
> Regards
> Alex
>
> ===
> diff --git a/fs/jbd/commit.c b/fs/jbd/commit.c
> index 34a4861..27ac2f3 100644
> --- a/fs/jbd/commit.c
> +++ b/fs/jbd/commit.c
> @@ -294,7 +294,7 @@ void journal_commit_transaction(journal_t *journal)
> int first_tag = 0;
> int tag_flag;
> int i;
> - int write_op = WRITE_SYNC;
> + int write_op = WRITE;
>
> /*
> * First job: lock down the current transaction and wait for
> diff --git a/fs/jbd2/commit.c b/fs/jbd2/commit.c
> index f3ad159..69ff08e 100644
> --- a/fs/jbd2/commit.c
> +++ b/fs/jbd2/commit.c
> @@ -329,7 +329,7 @@ void jbd2_journal_commit_transaction(journal_t *journal)
> int tag_bytes = journal_tag_bytes(journal);
> struct buffer_head *cbh = NULL; /* For transactional checksums */
> __u32 crc32_sum = ~0;
> - int write_op = WRITE_SYNC;
> + int write_op = WRITE;
>
> /*
> * First job: lock down the current transaction and wait for
>
>


--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/