Date: Mon, 23 Aug 2010 12:16:34 -0700 From: Pyun YongHyeon <pyunyh@gmail.com> To: Andre Oppermann <andre@freebsd.org> Cc: adrian.chadd@gmail.com, freebsd-net@freebsd.org Subject: Re: 8.0-RELEASE-p3: 4k jumbo mbuf cluster exhaustion Message-ID: <20100823191634.GE1116@michelle.cdnetworks.com> In-Reply-To: <4C72C622.2070302@freebsd.org> References: <AANLkTikrbCFHz-CnuYcgH2JzpeH5hob0Aa2y5dwn3Hvv@mail.gmail.com> <AANLkTikYMU=wML_z=HDnkUF1PGYMVa1q-QWTrkxD%2B7EP@mail.gmail.com> <20100822222746.GC6013@michelle.cdnetworks.com> <AANLkTi=t%2BnG8isp1nf2aBec%2BFwomApNt0NBPO8LqZ%2B=9@mail.gmail.com> <4C724AD9.5020000@freebsd.org> <20100823175220.GB1116@michelle.cdnetworks.com> <4C72C622.2070302@freebsd.org>
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On Mon, Aug 23, 2010 at 09:04:02PM +0200, Andre Oppermann wrote: > On 23.08.2010 19:52, Pyun YongHyeon wrote: > >On Mon, Aug 23, 2010 at 12:18:01PM +0200, Andre Oppermann wrote: > >>On 23.08.2010 11:26, Adrian Chadd wrote: > >>>On 23 August 2010 06:27, Pyun YongHyeon<pyunyh@gmail.com> wrote: > >>> > >>>>I recall there was SIOCSIFCAP ioctl handling bug in bce(4) on 8.0 so > >>>>it might also disable IFCAP_TSO4/IFCAP_TXCSUM/IFCAP_RXCSUM when yo > >>>>disabled RX checksum offloading. But I can't explain how checksum > >>>>offloading could be related with the growth of 4k jumbo buffers. > >>> > >>>Neither can I! > >>> > >>>I'm trying to come up with a reproduction method that doesn't involve > >>>"put box on the internet, push clients through it, wait." > >> > >>Network drivers use 2k sized mbuf clusters on receive. So the problem > >>doesn't seem to be RX related. > >> > > > >bce(4) is special in this regards. The controller would allocate > >jumbo cluster on RX if jumbo frame is used. If header splitting is > >used, driver will use normal mbuf clusters. > > Didn't know that. > > >>The function that is called on a socket write is sosend_generic() which > >>makes use of m_getm2(). This function allocates mbuf chains with the > >>tightest packing it can achieve. It will make use 4k (page size) mbufs > >>as much as it can. This is where they come from. > >> > >>It seems the 4k clusters do not get freed back to the pool after they've > >>been sent by the NIC and dropped from the socket buffer after the ACK has > >>arrived. The leak must occur in one of these two places. The socket > >>buffer is unlikely as it would affect not just you but everyone else too. > >>Thus the mbuf freeing after DMA/tx in the bce(4) driver is the prime > >>suspect. > >> > > > >I know bce(4) has a couple of bug in TX path(wrong dma tag, lack of > >bus_dmamap_sync(9) etc) but this is the same code path with/without > >TX checksum offloading. This is one of reason why I still do not > >understand what's really happening here. TX checksum offloading may > >introduce additional frame processing time to fill internal FIFO to > >compute checksum before transmitting the frame to wire such that it > >can change timing of TX path. This timing change might trigger the > >TX path bug. It's just vague guessing though. > > Had a chat with Claudio@OpenBSD and he said that the bce(4) DMA engine > can only access the first 1GB of physical RAM and has to use bounce > buffers all the time. Maybe this is related. > Really? I don't remember I saw such a DMA address space limitation in data sheet. And I don't think Broadcom made such a horrible thing for controllers targeted for servers. The only limitation I know is BCM5708 is not able to handle DMA addresses greater than 40bits so bce(4) limits the DMA address space in DMA tag creation.home | help
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