linux-kernel - Re: Linux disk performance.

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <652016d30612202203h16331f96o2147872db3cb2d43@mail.gmail.com>
Date:	Thu, 21 Dec 2006 11:48:42 +0545
From:	"Manish Regmi" <regmi.manish@...il.com>
To:	"Bill Davidsen" <davidsen@....com>
Cc:	linux-kernel@...r.kernel.org, kernelnewbies@...linux.org
Subject: Re: Linux disk performance.

On 12/21/06, Bill Davidsen <davidsen@....com> wrote:
> >
> > But isn't O_DIRECT supposed to bypass buffering in Kernel?
> That's correct. But it doesn't put your write at the head of any queue,
> it just doesn't buffer it for you.
>
> > Doesn't it directly write to disk?
> Also correct, when it's your turn to write to disk...

But the only process accessing that disk is my application.

> > I tried to put fdatasync() at regular intervals but there was no
> > visible effect.
> >
> Quite honestly, the main place I have found O_DIRECT useful is in
> keeping programs doing large i/o quantities from blowing the buffers and
> making the other applications run like crap. If you application is
> running alone, unless you are very short of CPU or memory avoiding the
> copy to an o/s buffer will be down in the measurement noise.

Yes... my application does large amount of I/O. It actually writes
video data received from ethernet(IP camera) to the disk using 128 K
chunks.

> I had a news (usenet) server which normally did 120 art/sec (~480 tps),
> which dropped to about 50 tps when doing large file copies even at low
> priority. By using O_DIRECT the impact essentially vanished, at the cost
> of the copy running about 10-15% slower. Changing various programs to
> use O_DIRECT only helped when really large blocks of data were involved,
> and only when i/o clould be done in a way to satisfy the alignment and
> size requirements of O_DIRECT.
>
> If you upgrade to a newer kernel you can try other i/o scheduler
> options, default cfq or even deadline might be helpful.

I tried all disk schedulers but all had timing bumps. :(

> --
> bill davidsen <davidsen@....com>
>    CTO TMR Associates, Inc
>    Doing interesting things with small computers since 1979
>


-- 
---------------------------------------------------------------
regards
Manish Regmi

---------------------------------------------------------------
UNIX without a C Compiler is like eating Spaghetti with your mouth
sewn shut. It just doesn't make sense.
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/