On Thu, Sep 8, 2011 at 3:41 PM, Mark Salter <msalter@xxxxxxxxxx> wrote: > On Wed, 2011-08-31 at 20:35 +0100, Will Deacon wrote: >> On Wed, Aug 31, 2011 at 07:19:33PM +0100, Rob Herring wrote: >> > On 08/31/2011 12:51 PM, Will Deacon wrote: >> > > Another thing that Marc and I tried on OMAP4 was not bringing up the secondary >> > > CPU during boot (by commenting out most of smp_init). In this case, I/O >> > > performance was good until we tried to online the secondary CPU. The online >> > > failed but after that the I/O performance was certainly degraded. >> > > >> > >> > Was the SCU enabled at that point? One diff between nosmp boot and >> > offlining the 2nd core would be that the SCU remains enabled in the >> > latter case. I think the SCU does not get enabled for nosmp. >> >> Our rudimentary test (printing out the SCU control register during boot) >> showed that it *was* enabled for nosmp. I think this is due to the secure >> world having to do that on OMAP so it's probably not true for other >> platforms. > > I've done a little test and found that turning on the MMU of the second > core causes the problem to show up. I patched head.S so I stopped the > second core in an infinite loop just before turning on the MMU. The > system continues booting on core#0 and I see ~20MB/s with hdparm -t to > an attached usb disk. Same setup but with second core being stopped with > infinite loop just after MMU is enabled shows ~5MB/s. So whatever is > going wrong, its not because of anything the second core is doing beyond > turning on its MMU and doing an empty loop. what was the final take on the optimization? Excuse if i could not follow the whole thread - could someone summarize for the benefit of many. Thanks > > --Mark > > > > > _______________________________________________ > linux-arm-kernel mailing list > linux-arm-kernel@xxxxxxxxxxxxxxxxxxx > http://lists.infradead.org/mailman/listinfo/linux-arm-kernel > -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
