linux-kernel - Re: [performance bug] kernel building regression on 64 LCPUs machine

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Date:	Wed, 19 Jan 2011 10:03:26 +0800
From:	Shaohua Li <shaohua.li@...el.com>
To:	"Shi, Alex" <alex.shi@...el.com>, jack@...e.cz, tytso@....edu
Cc:	"czoccolo@...il.com" <czoccolo@...il.com>,
	"vgoyal@...hat.com" <vgoyal@...hat.com>,
	"jaxboe@...ionio.com" <jaxboe@...ionio.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"Chen, Tim C" <tim.c.chen@...el.com>
Subject: Re: [performance bug] kernel building regression on 64 LCPUs
 machine

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
> 
> 


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