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Date:	Wed, 06 Apr 2011 10:00:40 -0700
From:	Eric Sandeen <sandeen@...hat.com>
To:	Zeev Tarantov <zeev.tarantov@...il.com>
CC:	Andreas Dilger <adilger@...ger.ca>,
	ext4 development <linux-ext4@...r.kernel.org>
Subject: Re: [PATCH] e2fsprogs: don't set stripe/stride to 1 block in mkfs

On 4/5/11 11:51 PM, Zeev Tarantov wrote:
> On Wed, Apr 6, 2011 at 01:21, Eric Sandeen <sandeen@...hat.com> wrote:
>> Zeev, if you'd like to test that patch above with your profiling, that'd be awesome.
> 
> My wall-clock timings are strange and I disregard them.
> On a desktop with X turned off and perf recording system-wide, I trust
> the profile to show everything.

Agreed, the wallclock time was just a very coarse sanity check while off at a conference :)

> In the no-stride case, I don't think you've made it any worse.

it shouldn't even go down this path so I hope not ;)

> In the stripe=stride=1, it went from:
> 
> [ perf record: Woken up 13 times to write data ]
> [ perf record: Captured and wrote 3.163 MB perf.data (~138211 samples) ]
> # Events: 14K cycles
> #
> # Overhead         Command          Shared Object
>              Symbol
> # ........  ..............  .....................
> .......................................
> #
>     13.08%            gzip  gzip                   [.] zip
>     12.65%     flush-253:0  [kernel.kallsyms]      [k] ext4_mb_scan_aligned

...

> to:
> 
> [ perf record: Woken up 12 times to write data ]
> [ perf record: Captured and wrote 3.091 MB perf.data (~135042 samples) ]
> # Events: 13K cycles
> #
> # Overhead      Command          Shared Object
>         Symbol
> # ........  ...........  .....................
> .....................................
> #
>     15.10%         gzip  gzip                   [.] zip
>     14.70%         gzip  gzip                   [.] treat_file.part.4.2264
>     11.10%  flush-253:0  [csnappy_compress]     [k] snappy_compress_fragment
>      6.12%       md5sum  md5sum                 [.] digest_file.isra.2.2089
...
>      0.23%             tar  [kernel.kallsyms]      [k] ext4_mb_scan_aligned
...

> So that's great, but I still don't want mke2fs to set a stripe and
> stride of 1, because that's silly - no code improvement in the
> allocator is ever going to be able to use that information.

I totally agree, and I'm sure the mkfs patch will go in as well.

Thanks for the verification of the kernel patch, too.

It should help a bit for sane stripe-sizes, too, with less impact as the stripe size gets bigger.

Thanks,
-Eric

>> Thanks,
>> -Eric
> 
> Thank you!
> -Z.T.

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