Dave, Zach,
thanks for your help, I've implemented a file descriptor passing mechanism
very similar to that of Zach's and it worked.
The problem now is performance, fd passing is utterly slow!
On my system (a 1GHz Pentium III + 2G RAM) I can do 1300 SpecWeb99 with a
khttp-like socket passing mechanism, while I only get something like 500 using
file descriptor passing. Indeed with fd passing I decrease Apache's
performance instead of increasing it!
I've checked my code several times and I don't believe that I have introduced
any specific bottleneck of my own (the code actually is quite trivial).
I've profiled the kernel and some interesting differences show:
With direct socket passing, 1300 SpecWeb load:
9759 total 0.0071
902 handle_IRQ_event 7.5167
256 skb_clone 0.6957
256 do_tcp_sendpages 0.0954
239 tcp_v4_rcv 0.1572
238 schedule 0.1766
226 __kfree_skb 0.9741
207 skb_release_data 1.7845
204 tcp_transmit_skb 0.1541
199 d_lookup 0.6910
190 path_walk 0.0973
181 ip_output 0.6754
168 fget 2.2105
165 do_softirq 1.1786
158 do_generic_file_read 0.1287
With file descriptor passing, 500 SpecWeb load:
8621 total 0.0063
7037 schedule 5.2203
462 handle_IRQ_event 3.8500
188 __wake_up 0.9216
114 unix_stream_data_wait 0.4191
81 __switch_to 0.3750
58 schedule_timeout 0.3718
25 d_lookup 0.0868
20 skb_clone 0.0543
19 path_walk 0.0097
17 tcp_transmit_skb 0.0128
17 do_tcp_sendpages 0.0063
17 do_softirq 0.1214
15 system_call 0.2679
15 sys_rt_sigtimedwait 0.0207
Zach, have you ever noticed such a performance bottleneck in your phhttpd?
SpecWeb has about 30% of its load as dynamic requests, so the amount of
forwarding is definitively significative in my case. Sime time ago I measured
khttp's impact in socket passing and I found that it was negligible
(forwarding everything to Apache instead of having it directly listening on
the socket had an impact of a few percent).
My impression from a first look to the profiling data is that the kernel is
doing a very poor job of scheduling and is ping-ponging between processes...
like it is not doing any buffering whatsoever and it is doing a contect switch
for every passed file descriptor.
Any thoughts?
- Fabio
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This archive was generated by hypermail 2b29 : Fri Mar 23 2001 - 21:00:19 EST