Date: Tue, 15 Jan 2013 21:43:54 -0800 From: Jack Vogel <jfvogel@gmail.com> To: Luigi Rizzo <rizzo@iet.unipi.it> Cc: "freebsd-net@freebsd.org" <freebsd-net@freebsd.org>, head@freebsd.org Subject: Re: two problems in dev/e1000/if_lem.c::lem_handle_rxtx() Message-ID: <CAFOYbc=47CWhXw=Gb299BfgW8G_uCSAJC0EYeB4jc8ZBLFYL-g@mail.gmail.com> In-Reply-To: <CA%2BhQ2%2BjEETBeN%2BHx=5aThr3pzcuK2L-%2BRd3cd1qDnYR67WSyxA@mail.gmail.com> References: <CA%2BhQ2%2BjEETBeN%2BHx=5aThr3pzcuK2L-%2BRd3cd1qDnYR67WSyxA@mail.gmail.com>
next in thread | previous in thread | raw e-mail | index | archive | help
OK, will look at this as soon as I can. Jack On Tue, Jan 15, 2013 at 5:23 PM, Luigi Rizzo <rizzo@iet.unipi.it> wrote: > Hi, > i found a couple of problems in > dev/e1000/if_lem.c::lem_handle_rxtx() , > (compare with dev/e1000/if_em.c::em_handle_que() for better understanding): > > 1. in if_em.c::em_handle_que(), when em_rxeof() exceeds the > rx_process_limit, the task is rescheduled so it can complete the work. > Conversely, in if_lem.c::lem_handle_rxtx() the lem_rxeof() is > only run once, and if there are more pending packets the only > chance to drain them is to receive (many) more interrupts. > > This is a relatively serious problem, because the receiver has > a hard time recovering. > > I'd like to commit a fix to this same as it is done in e1000. > > 2. in if_em.c::em_handle_que(), interrupts are reenabled unconditionally, > whereas lem_handle_rxtx() only enables them if IFF_DRV_RUNNING is set. > > I cannot really tell what is the correct way here, so I'd like > to put a comment there unless there is a good suggestion on > what to do. > > Accesses to the intr register are race-prone anyways > (disabled in fastintr, enabled in the rxtx task without > holding any lock, and generally accessed under EM_CORE_LOCK > in other places), and presumably enabling/disabling the > interrupts around activations of the taks is just an > optimization (and on a VM, it is actually a pessimization > due to the huge cost of VM exits). > > cheers > luigi >
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?CAFOYbc=47CWhXw=Gb299BfgW8G_uCSAJC0EYeB4jc8ZBLFYL-g>