Date: Thu, 5 Dec 2013 10:29:50 -0800 From: Adrian Chadd <adrian@freebsd.org> To: Yong-Hyeon Pyun <pyunyh@gmail.com> Cc: Jack F Vogel <jfv@freebsd.org>, Michael Tuexen <Michael.Tuexen@lurchi.franken.de>, "freebsd-net@freebsd.org list" <freebsd-net@freebsd.org> Subject: Re: A small fix for if_em.c, if_igb.c, if_ixgbe.c Message-ID: <CAJ-Vmo=kfoPMYjZ0WAtqmoJMz1utXH50SW9N92RA83EMUzY7WA@mail.gmail.com> In-Reply-To: <20131203021658.GC2981@michelle.cdnetworks.com> References: <521B9C2A-EECC-4412-9F68-2235320EF324@lurchi.franken.de> <20131202022338.GA3500@michelle.cdnetworks.com> <B9593E83-E687-49E9-ABDC-B2DD615180E9@lurchi.franken.de> <20131203021658.GC2981@michelle.cdnetworks.com>
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Hi, Yes. Looking at the ixgbe code, ixgbe_mq_start_locked() returns an error from ixgbe_xmit() but if it fails, it puts the buffer back. But it's already successfully queued a frame to the driver, so in this instance it shouldn't return the error from ixgbe_mq_start_locked(). The same deal in if_em.c and igb.c Now, drbr_putback() used to fail and now it doesn't, as you've said. So we should change the xxx_mq_start_locked() to set err=0 if we go via the drbr_putback() routine, as it hasn't actually failed to transmit. Now the very dirty thing is this - the error from xxx_transmit() is for the mbuf being queued at the end; but xxx_mq_start_locked() failures are for transmitting from the front. If there's only packet in the queue and that fails then they're the same thing and returning the error from xxx_mq_start_locked() matches the current mbuf being queued. But otherwise, they're referring to totally different packets. For TCP this may hurt; the TCP stack treats ENOBUFS a certain way and kicks off a timer to schedule a retransmit. I don't think we can fix _this_ right now. So Michael - can you redo your patch to set err=0 if drbr_putback() is called, and retest? Thanks! -adrian
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