Re: poor sata performance on 2.6

[Prakash K. Cheemplavam]

Jeff Garzik wrote:
> Denis Vlasenko wrote:
>
> > On Thursday 15 April 2004 17:48, Konstantin Sobolev wrote:
> >
> > > On Thursday 15 April 2004 18:33, Justin Cormack wrote:
> > >
> > > > On Thu, 2004-04-15 at 15:26, Konstantin Sobolev wrote:
> > > >
> > > > > On Thursday 15 April 2004 18:00, Justin Cormack wrote:
> > > > >
> > > > > > hmm, odd. I get 50MB/s or so from normal (7200, 8MB cache) WD disks,
> > > > > > and Seagate from the same controller. Can you send lspci,
> > > > > > /proc/interrupts and dmesg...
> > > > >
> > > > >
> > > > > Attached are files for 2.6.5-mm5 with highmem, ACPI and APIC turned
> > > > > off.
> > > >
> > > >
> > > > ah. Make a filesystem on it and mount it and try again. I see you have
> > > > no partition table and so probably no filesystem. This means the block
> > > > size is set to default 512byte not 4k which makes disk operations slow.
> > > > Any filesystem should default to block size of 4k, eg ext2.
[snip]
> > > So first time it gave the same loosy 27 MB/s and subsequent tests give
> > > pretty good 68 MB/s! Why?
> >
> >
> >
> > Time to CC ide/libata/block layer folks
> >
> > Jeff Garzik <jgarzik@xxxxxxxxx>
> >     libata man
>
>
>
> It seems like the situation is already resolved, to me.
>
> When you mount a filesystem, it changes the default block size (512 or 
> 1024) to the filesystem block size, normally 4096.  This would certainly 
> increase the throughput.


Hi Jeff,

it is NOT resolved: I just tried libata again, and I can  observe the 
same behaviour: I just did a "cat /dev/sda >/dev/null" and watched 
gkrellm2 showing the throughoutput. The first tiem I do the cat I only 
got about 27mb/s, no matter how ong I waited, but all subsequent cat 
gave me about >60mb/s. So there is a tiny bug in libata, I guess, as 
when using the siimage.c ide driver, already the first cat gives me 
maximum throughoutput. I am using 2.6.5-mm4 based kernel. Filesystems 
were mounted/ I didn't change anything between first and secound cat.

bye,

Prakash
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