From: Neil Brown <neilb@suse.de>
To: Wolfgang Denk <wd@denx.de>
Cc: "Bill Davidsen" <davidsen@tmr.com>,
"Keld Jørn Simonsen" <keld@dkuug.dk>,
linux-raid@vger.kernel.org
Subject: Re: recommendations for stripe/chunk size
Date: Thu, 7 Feb 2008 16:46:52 +1100 [thread overview]
Message-ID: <18346.39756.292908.58065@notabene.brown> (raw)
In-Reply-To: message from Wolfgang Denk on Wednesday February 6
On Wednesday February 6, wd@denx.de wrote:
>
> We implemented the option to select kernel page sizes of 4, 16, 64
> and 256 kB for some PowerPC systems (440SPe, to be precise). A nice
> graphics of the effect can be found here:
>
> https://www.amcc.com/MyAMCC/retrieveDocument/PowerPC/440SPe/RAIDinLinux_PB_0529a.pdf
Thanks for the link!
<quote>
The second improvement is to remove a memory copy that is internal to the MD driver. The MD
driver stages strip data ready to be written next to the I/O controller in a page size pre-
allocated buffer. It is possible to bypass this memory copy for sequential writes thereby saving
SDRAM access cycles.
</quote>
I sure hope you've checked that the filesystem never (ever) changes a
buffer while it is being written out. Otherwise the data written to
disk might be different from the data used in the parity calculation
:-)
And what are the "Second memcpy" and "First memcpy" in the graph?
I assume one is the memcpy mentioned above, but what is the other?
NeilBrown
next prev parent reply other threads:[~2008-02-07 5:46 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2008-02-05 18:24 recommendations for stripe/chunk size Keld Jørn Simonsen
2008-02-05 19:19 ` Justin Piszcz
2008-02-06 19:22 ` Bill Davidsen
2008-02-06 20:25 ` Wolfgang Denk
2008-02-06 22:37 ` Bill Davidsen
2008-02-07 0:31 ` Keld Jørn Simonsen
2008-02-07 5:40 ` Iustin Pop
2008-02-07 9:58 ` Keld Jørn Simonsen
2008-02-07 5:51 ` Neil Brown
2008-02-07 5:46 ` Neil Brown [this message]
2008-02-07 8:49 ` Wolfgang Denk
2008-02-07 5:31 ` Neil Brown
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=18346.39756.292908.58065@notabene.brown \
--to=neilb@suse.de \
--cc=davidsen@tmr.com \
--cc=keld@dkuug.dk \
--cc=linux-raid@vger.kernel.org \
--cc=wd@denx.de \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).