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. --Mark -- To unsubscribe from this list: send the line "unsubscribe linux-omap" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
