On Sun, Apr 16 2000, Andrea Arcangeli wrote:
> >Are you sure that you don't introduce lots of SMP races, e.g. in drivers
> >that support multiple majors?
>
> Also drivers with multiple "queues" should be checked.
Yeah, I suspect that is what Manfred meant.
> In all cases I'd prefer to get the patches separated in little pieces. The
> most interesting part is the get_request complexity fixage without the
> per-queue freelist but with two gloabl freelists. The other parts are more
> scalability changes than real fixes and they are completly orthogonal with
> the get_request fixage. get_request complexity always bitten us also doing
> I/O to only one disk in the system and fixing that things has more prio
> IMHO :).
Alright, I can see how that would be advantageous. Attached is the
proposed patch for stock 2.3.99-pre6-3 which does just that - two
request free lists and changes none of the locking changes.
I agree that the "big" patch is a 2.5 thing, this one should be
completely safe though. get_request tries to be more clever (and quick),
but some of that is lost with the light-weight patch because we must
provide a separate request table for loop and nbd.
> About the per-queue freelist thing, to allocate the requests I suggest to
> create a slab cache and allocating each request from the cache. The
> current big kmalloc wouldn't be reliable with modules.
I've meant to do this but decided it was a secondary issue. I've changed
this now, not for the attached patch though (not an issue).
> the lo->queue_head is a nbd internal queue and it's serialized by the
> down(&lo->queue_lock) so you don't need and you must not grab the
> io_request_lock there. The current code is correct.
Ok, thanks.
-- * Jens Axboe <axboe@suse.de> * Linux CD/DVD-ROM, SuSE Labs * http://kernel.dk
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This archive was generated by hypermail 2b29 : Sun Apr 23 2000 - 21:00:09 EST