Date: Thu, 13 Feb 2014 10:12:11 -0800 From: Scott Long <scott4long@yahoo.com> To: John-Mark Gurney <jmg@funkthat.com> Cc: FreeBSD Net <freebsd-net@freebsd.org>, Garrett Wollman <wollman@bimajority.org> Subject: Re: Use of contiguous physical memory in cxgbe driver Message-ID: <F442F22E-B8E2-4D63-B5C4-E4BBD892693E@yahoo.com> In-Reply-To: <20140213180736.GA34851@funkthat.com> References: <21216.22944.314697.179039@hergotha.csail.mit.edu> <201402111348.52135.jhb@freebsd.org> <CAJ-VmonCdNQPUCQwm0OhqQ3Kt_7x6-g-JwGVZQfzWTgrDYfmqw@mail.gmail.com> <201402121446.19278.jhb@freebsd.org> <21244.20212.423983.960018@hergotha.csail.mit.edu> <20140213075651.GY34851@funkthat.com> <21245.1163.754141.154430@hergotha.csail.mit.edu> <20140213180736.GA34851@funkthat.com>
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On Feb 13, 2014, at 10:07 AM, John-Mark Gurney <jmg@funkthat.com> wrote: > Garrett Wollman wrote this message on Thu, Feb 13, 2014 at 12:44 -0500: >> <<On Wed, 12 Feb 2014 23:56:51 -0800, John-Mark Gurney <jmg@funkthat.com> said: >> >>> Though we might want to keep a few mbufs reserved for receive now that >>> you mention it... We should never get to the point where we can't >>> allocate even one frame for receive... >> >> It's very easy to get to that state if the driver insists on getting >> three physically contiguous pages (which is what it takes to allocate >> a single 9k cluster) > > Well, if you're using a cheap NIC that can't do scatter/gather DMA, > then you get what you pay for… > Like I alluded to in another email, it’s not a hard problem to address for these “cheap” cards, it’s a deliberate design decision from FreeBSD. Scott
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