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From Greg Ames <grega...@remulak.net>
Subject Re: load spikes revisited
Date Fri, 18 Jan 2002 04:08:37 GMT
Aaron Bannert wrote:

got my nose out of the ktraces finally, so I re-read this a little closer.
 
> A quick glance at sendfile_it_all in server/core.c looks to me
> like it would loop repeatedly on that error condition, as we are seeing
> it in the ktrace output. 

No, you have to look at how sendfile_it_all interacts with apr_sendfile and the
kernel.  It blocks in select() until the kernel is happy with the amount of room
in its socket buffers.  Then the select returns to apr_sendfile, which issues
the next sendfile which will send some data (a multiple of 4k usually on
daedalus) but returns with -1 errno 35 anyway.  We change the retval to 0,
forget that the kernel warned us about blocking, and unwind to sendfile_it_all. 
It updates its offset and length to account for what was sent, and calls
apr_sendfile again.  apr_sendfile issues another sendfile right away, which is
almost always doomed to get -1 errno 35 with no bytes sent.  (This unproductive
sendfile call could be eliminated by remembering that the kernel told us it
would block across apr_sendfile invocations.)  Then we call select and block and
start over.

Greg

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