On Mon, 2011-02-14 at 11:34 +0000, Ben Hutchings wrote: > On Mon, 2011-02-14 at 11:23 +0100, Bastian Blank wrote: > > Hi folks > > > > I'd like to drop the i686 non-pae kernel. Currently we have sometimes > > -686 with PAE; only the normal kernel is without PAE. I'd like to get > > rid of this problem. Also this enables the use of the NX bit if supported > > by the CPU. > > > > There are some i686 processors without PAE support. This are some of the > > Pentium M (all of the Banias line and some of the Dothan line) and the > > Via C3 Nehemiah. All of them are released 2005 and earlier. > > Also Geode LX. > > Are there any changes we could/should make to the 486 flavour that would > make it perform better on 686-class processors? Should we consider also > dropping 486 support and making it a 586 flavour with corresponding > optimisations? [...] Before we make a change, I wanted to do a little testing to see whether running the 486 flavour is likely to hurt performance on the 686-class processors without PAE. And I do mean a little testing - I don't want to spend time constructing complex benchmarks. On my home server, which has one of the affected processors, specifically a VIA C3 "Nehemiah", I ran a simple benchmark for filesystem access: for i in $(seq 0 100); do \time find /usr >/dev/null; done and took the 'system' times from all but the first iteration (i.e. only the cache-hot case). I then compared these data sets with 'ministat': x 486 + 686 +------------------------------------------------------------------------------+ | x + | | x + + | | x + + | | x + + + | | x + * + | | x x x + * + | | x x x + * + | | x * x x + * + + | | x * x * + * + + | | x * * * + * + + | | x * * * * * + + + | | x * * * * * + * + | | x * * * * * + * + | | x * * * * * * * + + | | x x * * * * * * * + + | | * * * * * * * * * + + | |x * * * * * * * * * + * +| | |___________AM___________| | | |______________A_M____________| | +------------------------------------------------------------------------------+ N Min Max Median Avg Stddev x 100 0.27 0.38 0.32 0.3192 0.021304905 + 100 0.28 0.4 0.34 0.336 0.02502524 Difference at 95.0% confidence 0.0168 +/- 0.0064417 5.26316% +/- 2.01808% (Student's t, pooled s = 0.0232396) For this limited test, the 486 kernel actually seems to be slightly faster. Note that this was *not* run on an idle system, so other activity could affect the measurements a little. The Pentium M processors are likely to have different performance characteristics so I would like to see someone test them as well. It might be worth doing some kind of networking benchmark too. Ben. -- Ben Hutchings Once a job is fouled up, anything done to improve it makes it worse.
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