Re: poor sata performance on 2.6

Prakash K. Cheemplavam
2004-04-20T12:43:25Z

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@pobox.com>
>> 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