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Date: Mon, 22 Sep 2008 10:04:25 +0530 From: Krishna Kumar <krkumar2@...ibm.com> To: linux-kernel@...r.kernel.org Cc: Andrew Morton <akpm@...ux-foundation.org>, Krishna Kumar <krkumar2@...ibm.com> Subject: [RFC] [PATCH 0/1] timers: add_timer should never be called if pending From: Krishna Kumar <krkumar2@...ibm.com> (Hopefully this is not something that has been suggested earlier and rejected). add_timer should never be called on a pending timer - such bugs should be caught by reports generated by debug kernels. It is the responsibility of the subsystem users to ensure that timers are not added twice. Using the add_timer_on interface reduces the code that checks if the timer is pending, the timer_base change, updating 'expires' two times, etc. 1. Single CPU, Single Timer: Add the same timer serially on one CPU - do this many times. Laptop (2 way Xeon): Saves 10.8% ORG: Time: 35359 NEW: Time: 31527 Server (4 way x86-64): Saves 7.9% ORG: Time: 4520 NEW: Time: 4164 2. Single CPU, Multiple Timer: Add different timers serially on one CPU - do this many times. Laptop (2 way Xeon): Saves 7.7% ORG: Time: 133728 NEW: Time: 144822 Server (4 way x86-64): Saves 15.7% ORG: Time: 69012 NEW: Time: 58186 3. Many CPU's, Single Timer: Add the same timer in parallel on all CPUs - do this many times. Laptop (2 way Xeon): Saves 14% ORG: Time: 69845 NEW: Time: 60067 Server (4 way x86-64): Saves 21.8% ORG: Time: 18047 NEW: Time: 14116 4. Many CPU's, Multiple Timer: Add different timers in parallel on all CPUs - do this many times. Laptop (2 way Xeon): Saves 47.1% ORG: Time: 292173 NEW: Time: 154485 Server (4 way x86-64): Saves 8.23 ORG: Time: 319129 NEW: Time: 292842 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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