Re: -rc7 Re: Linux 2.4.21-rc6

[Nick Piggin]

Jens Axboe wrote:

>On Wed, Jun 04 2003, Nick Piggin wrote:
>
>>Andrea Arcangeli wrote:
>>
>>
>>>On Wed, Jun 04, 2003 at 12:46:33PM +0200, Marc-Christian Petersen wrote:
>>>
>>>
>>>>On Wednesday 04 June 2003 12:42, Jens Axboe wrote:
>>>>
>>>>Hi Jens,
>>>>
>>>>
>>>>
>>>>>>>the issue with batching in 2.4, is that it is blocking at 0 and waking
>>>>>>>at batch_requests. But it's not blocking new get_request to eat
>>>>>>>requests in the way back from 0 to batch_requests. I mean, there are
>>>>>>>two directions, when we move from batch_requests to 0 get_requests
>>>>>>>should return requests. in the way back from 0 to batch_requests the
>>>>>>>get_request should block (and it doesn't in 2.4, that is the problem)
>>>>>>>
>>>>>>>
>>>>>>do you see a chance to fix this up in 2.4?
>>>>>>
>>>>>>
>>>>>Nick posted a patch to do so the other day and asked people to test.
>>>>>
>>>>>
>>>>Silly mcp. His mail was CC'ed to me :( ... F*ck huge inbox.
>>>>
>>>>
>>>I was probably not CC'ed, I'll search for the email (and I was
>>>travelling the last few days so I didn't read every single l-k email yet
>>>sorry ;)
>>>
>>>
>>>
>>The patch I sent is actually against 2.4.20, contrary to my
>>babling. Reports I have had say it helps, but maybe not so
>>much as Andrew'ss fixes. Then Matthias Mueller ported my patch
>>to 2.4.21-rc6 which include Andrew's fixes.
>>
>>It seems that they might be fixing two different problems.
>>It looks promising though.
>>
>
>It is a different problem I think, yours will fix the starvation of
>writers (of readers, writers is much much easier to trigger though)
>where someone will repeatedly get cheaten by the request allocator.
>
>The other problem is still not clear to anyone. I doubt this patch would
>make any difference (apart from a psychological one) in this case,
>since you have a single writer and maybe a reader or two. The single
>writer cannot starve anyone else.
>

You are right about what the patch does. It wouldn't surprise me
if there are still other problems, but it could be that the reader
has to write some swap or other dirty buffers when trying to get
memory itself.

I have had 3 or so reports all saying similar things, but it could
be psychological I guess.