On 23.08.2010 21:16, Pyun YongHyeon wrote:
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:
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 clau...@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.
Oops... OpenBSD bce(4) != FreeBSD bce(4). The former is for BCM440x
chips the latter for BCM57xx.
--
Andre
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