Re: very low performance on SCSI disks if device node is in tmpfs

[Andrew Morton]

Andrew Morton <akpm@xxxxxxxx> wrote:
>
> Olaf Hering <olh@xxxxxxx> 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.

It affects IDE too - the context switch and interrupt rates are through the
roof.  IDE disks have always seemed better at doing readahead, which is why
the transfer bandwidth is much the same.

Everything there is consistent with "not doing readahead".  The fickle
finger points in the general direction of fs/block_dev.c:do_open().  Later.
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