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I run 3 diald processes on a Linux box sitting on a pretty busy ethernet.
I recently noticed that each of these dialds was using 1-3% cpu time, even
when the proxies were idle. Turning on promisc mode on eth0 pushed that
through the roof. 'strace'ing a diald produced results along the line of:
select(100, [1 2 4], NULL, NULL, {0, 990000}) = 1 (in [2], left {0, 710000})
recvfrom(2, "\377\377\377\377\377\377\252\0\4"..., 4096, 0,
{sun_family=AF_UNIX, sun_path="eth0"}, [16]) = 142
time(NULL) = 842498155
time(NULL) = 842498155
select(100, [1 2 4], NULL, NULL, {0, 710000}) = 1 (in [2], left {0, 520000})
recvfrom(2, "\377\377\377\377\377\377\252\0\4"..., 4096, 0,
{sun_family=AF_UNIX, sun_path="eth0"}, [16]) = 111
time(NULL) = 842498155
time(NULL) = 842498155
select(100, [1 2 4], NULL, NULL, {0, 520000}) = 1 (in [2], left {0, 190000})
recvfrom(2, "\377\377\377\377\377\377\0\200\243"..., 4096, 0,
{sun_family=AF_UNIX, sun_path="eth0"}, [16]) = 110
time(NULL) = 842498155
time(NULL) = 842498155
(etc)
It looks like the snoop device is still receiving packets from eth0,
despite the fact that descriptor 2, a SOCK_PACKET socket, has successfully
called bind() to bind to the slip proxy.
Looking in net/core/dev.c, it looks like net_bh is forwarding packets that
it shouldn't - it forwards packets to a packet-capture function with
protocol ETH_P_ALL regardless of the value of ptype->dev.
I changed this to check the device, and the dialds magically went to 0%
cpu :) ... a patch is attached (against 2.0.14, but I didn't see any
changes to this bit of code in 15-18). I did a grep for ETH_P_ALL and the
kernel code doesn't seem to use it, so hopefully this doesn't break
anything else.
Is it worth moving the ptype_all list for sniffers bound to a specific
device into the device struct? The current setup means that such a sniffer
will cause a check of the entire ptype_all list for every packet received
on _any_ device - which could become a problem with eg. multiple dialds
(large ptype_all list) and a busy ethernet.
Oliver.
(oliver@sa-search.massey.ac.nz, in case sendmail decides to mangle it)
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