Messages in this thread | ![/](/images/icornerl.gif) | | Date | Tue, 1 Apr 2003 12:47:12 +0200 | From | Jens Axboe <> | Subject | Re: [PATCH] rq-dyn-alloc, dynamic request allocation |
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On Tue, Apr 01 2003, Andrew Morton wrote: > Jens Axboe <axboe@suse.de> wrote: > > > > Hi, > > > > This patch adds dynamic request allocation to the block io path. On > > systems with lots of disks (and thus queues) it saves a non-significant > > amount of low memory. It also allows for much better experimentation > > with larger queue lengths, this experimental patch tops the queue depth > > off at 16384 (vs 128 before). > > heh, 16k requests per queue? Last time I played with 1024 certain popular > benchmarks ran like a bullet.
I have one such unmentionable benchmark running right now, current depth is 5127 :-)
> > Please play with it. Andrew, want a version for -mm? > > Would be much appreciated, thanks.
Ok, getting on it.
> > */ > > static struct request *get_request_wait(request_queue_t *q, int rw) > > { > > - DEFINE_WAIT(wait); > > - struct request_list *rl = &q->rq[rw]; > > struct request *rq; > > > > - spin_lock_prefetch(q->queue_lock); > > - > > generic_unplug_device(q); > > do { > > - int block = 0; > > + rq = get_request(q, rw, GFP_NOIO); > > > > - prepare_to_wait_exclusive(&rl->wait, &wait, > > - TASK_UNINTERRUPTIBLE); > > - spin_lock_irq(q->queue_lock); > > - if (!rl->count) > > - block = 1; > > - spin_unlock_irq(q->queue_lock); > > - > > - if (block) > > + if (!rq) > > io_schedule(); > > hmm. I fear that if a SCHED_FIFO/SCHED_RR task hits this, it will just pick > itself to run again in the schedule() and the box locks up. > > A blk_congestion_wait(WRITE, HZ/50) may be better here. It will send the > caller to sleep until someone puts a write request back, which seems > appropriate.
Yes good point, I'll make that change.
-- Jens Axboe
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