Messages in this thread | | | Date | Fri, 07 Sep 2007 07:24:43 -0700 | From | Randy Dunlap <> | Subject | Re: [patch 8/8] Immediate Values - Documentation |
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Mathieu Desnoyers wrote: > * Randy Dunlap (randy.dunlap@oracle.com) wrote: > [fixing the rest of the comments in the patch] >> What character is this that I cannot read (not displayed properly >> by my email client maybe)? <something> after 644.09 and before the >> +- symbol, repeated just before all of the +- symbols. >> > > This file seems to be UTF-8 and the mail has been send by quilt. Is it > ok or should I change this to +/- just to make sure ?
I think that most people on lkml say that UTF-8 is OK in text doc files.
>>> +Getppid without memory pressure: >>> +1462.09±18.87 - 150.92±1.01 = 1311.17±18.90 cycles >>> + >>> +Getppid with memory pressure: >>> +17113.33±1655.92 - 578.22±269.51 = 16535.11±1677.71 cycles >>> + >>> +Therefore, if we add 2 markers not based on immediate values to the getppid >>> +code, which would add 2 memory reads, we would add >>> +2 * 555.93±12.74 = 1111.86±25.48 cycles >>> + >>> +Therefore, >>> + >>> +1111.86±25.48 / 16535.11±1677.71 = 0.0672 >>> + relative error: sqrt(((25.48/1111.86)^2)+((1677.71/16535.11)^2)) >>> + = 0.1040 >>> + absolute error: 0.1040 * 0.0672 = 0.0070 >>> + >>> +Therefore: 0.0672±0.0070 * 100% = 6.72±0.70 % >>> + >>> +We can therefore affirm that adding 2 markers to getppid, on a system with high >>> +memory pressure, would have a performance hit of at least 6.0% on the system >>> +call time, all within the uncertainty limits of these tests. The same applies to >>> +other kernel code paths. The smaller those code paths are, the highest the >>> +impact ratio will be. >>> + >>> +Therefore, not only is it interesting to use the immediate values to dynamically >>> +activate dormant code such as the markers, but I think it should also be >>> +considered as a replacement for many of the "read mostly" static variables.
-- ~Randy *** Remember to use Documentation/SubmitChecklist when testing your code *** - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.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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