Darius D. wrote: > > > Does Tomcat APR really needs pollTime set so low by default? I thought > timeout is meant for some sort of book keeping, where is all connections > in FD set are "idle", no events come for timeout period - you force > timeout and do bookkeeping - on a busy system you will get events anyway > cause of socket traffic. Also connection timeout is 60s by default, so > ending connection @ 2ms precision is not enhancing latency in any way. > > I think defaults should be increased to something reasonable like 100ms > (pollTime ="100000") to avoid unneeded wakeups (and wakeups are bad, cause > they cause context switch, and context switches pollute caches, TLB > buffers and on modern servers burn electricity by forcing CPUs from low C > states ) > >
I guess there is no interest in efficiency and reducing overhead with APR connectors? Overhead is quite substantial. Consider the following - on a lightly loaded system we were seeing ~1.8k timer interrups and context switches with Linux 2.6.39 kernel and latest Tomcat 7 + 1.20 TCNative + APR. And its easy to see where from they are coming - 3 connector (AJP 8009, HTTP, HTTPS) , all APR, all 2000 microseconds PollTime. So we were getting ~500x3 context switches from all those epoll_wait(...,2ms) calls. And they were just burning CPU and polluting caches. After switching to NIO connectors on same system and same load CS and interrupts are down to ~600. ( note that to reproduce this you need a system with NO_HZ kernel and HPET to actually get a epoll_wait timeout of 2000us instead of ~1/HZ (10ms on 100HZ kernel ) minimum on normal kernels ) I have attached screenshot from munin irq stats display. http://old.nabble.com/file/p32115035/irqstats-week.png irqstats-week.png So results are pretty obviuos. -- View this message in context: http://old.nabble.com/APR-connector-pollTime-defaults-are-strange-in-tomcat6-7-tp32085364p32115035.html Sent from the Tomcat - User mailing list archive at Nabble.com. --------------------------------------------------------------------- To unsubscribe, e-mail: users-unsubscr...@tomcat.apache.org For additional commands, e-mail: users-h...@tomcat.apache.org
