Re: Slow ICP under high loads (squid-1.2beta20 & 21)

Stewart Forster <slf@connect.com.au> writes:

> For some time now I've been encountering very slow ICP responses from caches
> under high load (sustained > 30 TCP & > 100 ICP requests/sec). I've managed
> to trace this down to some code that was added a little while ago in the
> effort to reduce CPU usage.

Hmmm. I think the issue is more that icpHandleUdp() will only read one
packet each time it's called. Changing icpHandleUdp to loop unto the
recvfrom() returns EAGAIN is probably a better fix. (certainly, it's
much cheaper on the CPU).

Looking at the code, httpAccept() should possibly do the same thing.

It should result in the same thruput, but with a lower CPU
overhead. (and I think you're suffering the same CPU problem we are,
aren't you? )

A dumb patch for ipc_v2 follows... (checks that it compiles, not that
it works.. :) (this also handles the case where recvfrom returns
0. Not sure if this is possible, but I'm a little paranoid)

Michael.

--- ipc_v2.c.old Wed May 27 09:42:39 1998
+++ icp_v2.c Wed May 27 09:43:31 1998
@@ -307,6 +307,7 @@
     int icp_version;
 
     commSetSelect(sock, COMM_SELECT_READ, icpHandleUdp, NULL, 0);
+ again:
     from_len = sizeof(from);
     memset(&from, '\0', from_len);
     len = recvfrom(sock,
@@ -315,14 +316,15 @@
        0,
        (struct sockaddr *) &from,
        &from_len);
- if (len < 0) {
+ if (len < 1) {
 #ifdef _SQUID_LINUX_
        /* Some Linux systems seem to set the FD for reading and then
         * return ECONNREFUSED when sendto() fails and generates an ICMP
         * port unreachable message. */
        /* or maybe an EHOSTUNREACH "No route to host" message */
- if (errno != ECONNREFUSED && errno != EHOSTUNREACH)
+ if (len<0 && errno != ECONNREFUSED && errno != EHOSTUNREACH)
 #endif
+ if (len<0 && errno != EAGAIN)
            debug(50, 1) ("icpHandleUdp: FD %d recvfrom: %s\n",
                sock, xstrerror());
        return;
@@ -350,6 +352,7 @@
            icp_version,
            inet_ntoa(from.sin_addr),
            ntohs(from.sin_port));
+ goto again;
 }
 
 void
Received on Tue Jul 29 2003 - 13:15:50 MDT