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Message-ID: <20061222173220.GU17199@kernel.dk> Date: Fri, 22 Dec 2006 18:32:22 +0100 From: Jens Axboe <jens.axboe@...cle.com> To: Christoph Hellwig <hch@...radead.org>, Kiyoshi Ueda <k-ueda@...jp.nec.com>, agk@...hat.com, mchristi@...hat.com, linux-kernel@...r.kernel.org, dm-devel@...hat.com, j-nomura@...jp.nec.com Subject: Re: [RFC PATCH 1/8] rqbased-dm: allow blk_get_request() to be called from interrupt context On Fri, Dec 22 2006, Christoph Hellwig wrote: > On Wed, Dec 20, 2006 at 12:50:02PM -0500, Kiyoshi Ueda wrote: > > Because I'd like to use blk_get_request() in q->request_fn() > > which can be called from interrupt context like below: > > scsi_io_completion -> scsi_end_request -> scsi_next_command > > -> scsi_run_queue -> blk_run_queue -> q->request_fn > > > Or request should not be allocated in q->request_fn() anyway? > > Do you have any other ideas? > > The right long-term fix is to make sure request_fn is only ever called > from process context. This means moving retry handling to a thread instead > of a softirq, but this will need careful performance testing and tweaking. It's a lot more than just retry handling. Most driver reinvoke queueing from the completion handling, so basically most of the time request_fn is run from either softirq (like SCSI) or interrupt context (like IDE). -- Jens Axboe - 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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