Date: Mon, 12 Nov 2012 14:15:56 -0500 From: Karim <fodillemlinkarim@gmail.com> To: freebsd-net@freebsd.org Subject: em/igb if_transmit (drbr) and ALTQ Message-ID: <50A14AEC.2040303@gmail.com>
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Hi all, I have been following the current discussions on igb tx/rx locking with great interest and I though I would point out (as it was before pointed out in kern/138392) that any driver setting if_start to NULL and using if_transmit (multi-queue or not) will effectively break ALTQ. The reason for this can be found in tbr_timeout() in altq_subr.c where the token bucket regulator goes through all ALTQ registered interface and tries to 'kick' them into sending through if_start(). tbr_timeout() : ... for (ifp = TAILQ_FIRST(&V_ifnet); ifp; ifp = TAILQ_NEXT(ifp, if_list)) { /* read from if_snd unlocked */ if (!TBR_IS_ENABLED(&ifp->if_snd)) continue; active++; if (!IFQ_IS_EMPTY(&ifp->if_snd) && ifp->if_start != NULL) /* if_start is NULL if if_transmit is used in em/igb driver */ (*ifp->if_start)(ifp); } ... As you can see if_start is NULL on those new multi-queue enabled drivers which has for net effect to 'break' ALTQ's token bucket regulator. I am writing this because I am interested in your comments on how this can be fixed properly looking forward. The whole range of suggestions; from 'don't compile with EM_MULTIQUEUE defined' to 'here is how you can make ALTQ use drbr' will help. Thanks you, Karim.
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