From mboxrd@z Thu Jan 1 00:00:00 1970 From: root Date: Tue, 12 Jun 2001 16:23:32 +0000 Subject: Re: [Linux-ia64] IO/TLB bounce buffer space Message-Id: List-Id: References: In-Reply-To: MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: linux-ia64@vger.kernel.org >>>>> On Tue, 12 Jun 2001 10:44:12 +0200 (CEST), Martin Wilck said: Martin> it is becoming apparent that the limited bounce buffer space Martin> is the reason for the crashes with the new aic7xxx driver Martin> and linux-IA64 with >=4GB RAM that I reported previously. Martin> If I understand it right, the driver uses up to 253 buffers Martin> per device, each of which can be 8kB in size. Consequently, Martin> it almost completely fills up the available IO/TLB space. The deeper question is of course: is this really a good idea? From a latency perspective, such long queues may not make a lot of sense. Even from a throughput perspective the benefit of using a 253 entry queue is probably negligible compared to a shorter queue. Reading aic7xxx.h, I get the impression that the author chose 253 as the max queue length because s/he could. I don't see anything that suggests that this length is optimal in any sense. It might be worth experimenting with. Martin> Question: Would it hurt to increase IO/TLB space on machines Martin> with large memory? Would it be possible and make sense to Martin> make IO/TLB space size a kernel configuration option? An alternative is to use GFP_ATOMIC allocation. I'm not sure that counts as a "solution" though as it arguably just hides the real issue. --david