Messages in this thread |  | | | Date | Tue, 25 May 2004 14:48:36 -0700 | | From | Andrew Morton <> | | Subject | Re: very low performance on SCSI disks if device node is in tmpfs |
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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. - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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