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Message-ID: <20061012130907.GZ6515@kernel.dk> Date: Thu, 12 Oct 2006 15:09:07 +0200 From: Jens Axboe <jens.axboe@...cle.com> To: Vasily Tarasov <vtaras@...nvz.org> Cc: Linux Kernel Mailing List <linux-kernel@...r.kernel.org>, OpenVZ Developers List <devel@...nvz.org> Subject: Re: [PATCH] block layer: ioprio_best function fix On Thu, Oct 12 2006, Vasily Tarasov wrote: > Currently ioprio_best function first checks wethere aioprio or bioprio equals > IOPRIO_CLASS_NONE (ioprio_valid() macros does that) and if it is so it returns > bioprio/aioprio appropriately. Thus the next four lines, that set aclass/bclass > to IOPRIO_CLASS_BE, if aclass/bclass == IOPRIO_CLASS_NONE, are never executed. > > The second problem: if aioprio from class IOPRIO_CLASS_NONE and bioprio from > class IOPRIO_CLASS_IDLE are passed to ioprio_best function, it will return > IOPRIO_CLASS_IDLE. It means that during __make_request we can merge two > requests and set the priority of merged request to IDLE, while one of > the initial requests originates from a process with NONE (default) priority. > So we can get a situation when a process with default ioprio will experience > IO starvation, while there is no process from real-time class in the system. > > Just removing ioprio_valid check should correct situation. Analysis looks correct, thanks. -- 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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