From: Andrew Morton <akpm@osdl.org>
To: Olaf Hering <olh@suse.de>
Cc: linux-kernel@vger.kernel.org
Subject: Re: very low performance on SCSI disks if device node is in tmpfs
Date: Tue, 25 May 2004 14:48:36 -0700 [thread overview]
Message-ID: <20040525144836.1af59a96.akpm@osdl.org> (raw)
In-Reply-To: <20040525184732.GB26661@suse.de>
Olaf Hering <olh@suse.de> wrote:
>
> Any ideas why the location of the device node makes such a big
> difference? I always wondered why my firewire is so dog slow with 2.6.
> Now I know the reason: /dev is in tmpfs.
> I dont see that with IDE disks, only with SCSI.
This is truly bizarre. Reading /dev/sda I get 24MB/sec at 700 context
switches/sec. Reading /mnt/tmpfs/sda it's 14MB/sec, 7000 switches/sec.
/mnt/ramfs/sda is slow too. /mnt/hda5/sda is fast.
I'd assumed that the kernel got the backing_dev_info's screwed up and the
tmpfs node isn't doing readahead but that appears to not be the case
(/dev/sda is still fast with zero readahead).
You really, really get the weird-bug-of-the-month award for this one. I'll
poke at it some more later on.
next prev parent reply other threads:[~2004-05-25 21:47 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2004-05-25 18:47 Olaf Hering
2004-05-25 19:14 ` Richard B. Johnson
2004-05-25 19:34 ` Olaf Hering
2004-05-25 19:44 ` Richard B. Johnson
2004-05-25 20:02 ` Oliver Neukum
2004-05-25 21:48 ` Andrew Morton [this message]
2004-05-25 21:57 ` Richard B. Johnson
2004-05-25 21:59 ` Andrew Morton
2004-05-25 22:41 ` Andrew Morton
2004-05-26 0:05 ` Linus Torvalds
2004-05-26 0:10 ` viro
2004-05-26 0:14 ` Andrew Morton
2004-05-26 9:53 ` Olaf Hering
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