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Date: Mon, 02 Nov 2009 14:16:44 +0100 From: Eric Dumazet <eric.dumazet@...il.com> To: William Allen Simpson <william.allen.simpson@...il.com> CC: Linux Kernel Developers <linux-kernel@...r.kernel.org>, Linux Kernel Network Developers <netdev@...r.kernel.org> Subject: Re: [net-next-2.6 PATCH RFC] TCPCT part 1d: generate Responder Cookie William Allen Simpson a écrit : > Eric Dumazet wrote: >> cookie_hash() runs in a non preemptable context. CPU cannot change >> under us. >> >> (or else, we would not use __get_cpu_var(ipv4_cookie_scratch); ) >> >> And of course, each cpu gets its own scratch area, thanks to >> __get_cpu_var() >> > Interesting. I'm not sure that running CPU intensive functions like > SHA1 in > a non-preemptable context is a good idea. I'd assumed it wasn't! > > Perhaps you could point at the documentation in the code that explains > this? I suggest you read Documentations/ files about softirq http://docs.blackfin.uclinux.org/kernel/generated/kernel-hacking.xml Large part of network code is run by softirq handler, and a softirq handler is not preemptable with another softirq (including itself). > Perhaps a function header comment that mentions it? So we are going to add a header to thousand of functions repeating this prereq ? > > All I know is (from testing) that the tcp_minisockets.c caller is sometimes > called in a fashion that requires atomic allocation, and other times > does not! Maybe callers have different contexts (running from softirq handler or from process context). Atomic ops are expensive and we try to avoid them if/when possible. > > See my "Subject: query: tcpdump versus atomic?" thread from Oct 14th. You probably add a bug in your kernel, leaving a function with unpaired lock/unlock of notallow_something/allow_something There are books about linux internals that you could read if you want some extra documentation. Dont ask me details, I never read them :) -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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