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Date: Fri, 20 May 2011 08:40:56 +0800 From: Shaohua Li <shaohua.li@...el.com> To: "Alex,Shi" <alex.shi@...el.com> Cc: Jens Axboe <jaxboe@...ionio.com>, "James.Bottomley@...senpartnership.com" <James.Bottomley@...senpartnership.com>, "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org> Subject: Re: Perfromance drop on SCSI hard disk 2011/5/20 Alex,Shi <alex.shi@...el.com>: > On Fri, 2011-05-20 at 02:27 +0800, Jens Axboe wrote: >> On 2011-05-19 10:26, Alex,Shi wrote: >> > >> >> I will queue up the combined patch, it looks fine from here as well. >> >> >> > >> > When I have some time to study Jens and shaohua's patch today. I find a >> > simpler way to resolved the re-enter issue on starved_list. Following >> > Jens' idea, we can just put the starved_list device into kblockd if it >> > come from __scsi_queue_insert(). >> > It can resolve the re-enter issue and recover performance totally, and >> > need not a work_struct in every scsi_device. The logic/code also looks a >> > bit simpler. >> > What's your opinion of this? >> >> Isn't this _identical_ to my original patch, with the added async run of >> the queue passed in (which is important, an oversight)? > > Not exactly same. It bases on your patch, but added a bypass way for > starved_list device. If a starved_list device come from > __scsi_queue_insert(), that may caused by our talking recursion, kblockd > with take over the process. Maybe you oversight this point in original > patch. :) > > The different part from yours is below: > --- > static void __scsi_run_queue(struct request_queue *q, bool async) > { > struct scsi_device *sdev = q->queuedata; > struct Scsi_Host *shost; > @@ -435,30 +437,35 @@ static void scsi_run_queue(struct request_queue > *q) > &shost->starved_list); > continue; > } > - > - spin_unlock(shost->host_lock); > - spin_lock(sdev->request_queue->queue_lock); > - __blk_run_queue(sdev->request_queue); > - spin_unlock(sdev->request_queue->queue_lock); > - spin_lock(shost->host_lock); > + if (async) > + blk_run_queue_async(sdev->request_queue); > + else { > + spin_unlock(shost->host_lock); > + spin_lock(sdev->request_queue->queue_lock); > + __blk_run_queue(sdev->request_queue); > + spin_unlock(sdev->request_queue->queue_lock); > + spin_lock(shost->host_lock); >> I don't quite like this approach. blk_run_queue_async() could introduce fairness issue as I said in previous mail, because we drop the sdev from starved list but didn't run its queue immediately. The issue exists before, but it's a bug to me. Alex, is there any real advantage of your patch? Thanks, Shaohua -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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