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Date: Mon, 23 Nov 2009 10:58:52 +0100 From: Jesper Dangaard Brouer <jdb@...x.dk> To: Eric Dumazet <eric.dumazet@...il.com> Cc: Linux Kernel Network Hackers <netdev@...r.kernel.org>, Robert Olsson <robert@...julf.net> Subject: Strange CPU load when flushing route cache (kernel 2.6.31.6) Hi Eric and netdev, I have observed a strange route cache behaviour when I upgraded some of my production Linux routers (1Gbit/s tg3) to kernel 2.6.31.6 (from kernel 2.6.25.7). Every time the route cache is flushed I get a CPU spike (in softirq) with a tail. I have attached some graphs that illustrate the issue (hope vger.kernel.org will allow these attachments...) I have done some tuning of the route cache: # From /etc/sysctl.conf # # Adjusting the route cache flush interval net/ipv4/route/secret_interval = 1200 # Limiting the route cache size # ip_dst_cache slab objects is 256 bytes. # 2000000 * 256 bytes = 512 MB net/ipv4/route/max_size = 2000000 Boot parameters: "rhash_entries=262143 vmalloc=256M" The rhash_entries is for the route cache hash size. The vmalloc is needed because I have _very_ large iptables rulesets (and is running on a 32-bit kernel, due to old hardware). Any thoughs on how to avoid these CPU spikes? Or where the issue occurs in the code? -- Med venlig hilsen / Best regards Jesper Brouer ComX Networks A/S Linux Network Kernel Developer Cand. Scient Datalog / MSc.CS Author of http://adsl-optimizer.dk LinkedIn: http://www.linkedin.com/in/brouer Download attachment "CPU_usage.png" of type "image/png" (16710 bytes) Download attachment "CPU_usage_softirq.png" of type "image/png" (15344 bytes) Download attachment "PPS_eth1-rx.png" of type "image/png" (10930 bytes) Download attachment "route_cache.png" of type "image/png" (17499 bytes) Download attachment "softnet_time_squeeze.png" of type "image/png" (15145 bytes)
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