mav at FreeBSD.org
Mon Mar 22 05:53:21 UTC 2010
> On Sun, 21 Mar 2010 20:54, jhell@ wrote:
>> I played with it on one re-compile of a kernel and for the sake of it
>> DFLTPHYS=128 MAXPHYS=256 and found out that I could not cause a crash
>> dump to be performed upon request (reboot -d) due to the boundary
>> being hit for DMA which is 65536. Obviously this would have to be
>> adjusted in ata-dma.c.
>> I suppose that there would have to be a better way to get the real
>> allowable boundary from the running system instead of setting it
>> Other then the above I do not see a reason why not... It is HEAD and
>> this is the type of experimental stuff it was meant for.
> I should have also said that I also repeated the above without setting
> DFLTPHYS and setting MAXPHYS to 256.
It was bad idea to increase DFLTPHYS. It is not intended to be increased.
About DMA boundary, I do not very understand the problem. Yes, legacy
ATA has DMA boundary of 64K, but there is no problem to submit S/G list
of several segments. How long ago have you tried it, on which controller
and which diagnostics do you have?
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