Re: [PATCH 1/5] util, resctrl: using 64bit interface instead of 32bit for counters

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On 2019/12/16 下午6:12, Daniel P. Berrangé wrote:
On Sun, Dec 15, 2019 at 02:39:20AM +0000, Wang, Huaqiang wrote:
Hi Daniel,

Thanks for your review.

About patch 1/5, I understand we should be very cautious when we changes  the determined
interface.

I'd like to reserved the old 32bit interface  and propose a new 64bit interface just as you
suggested if you still think so after you  got my intention.
Here actually I want to fix a bug, maybe I should title this patch as *bug fixing*. Reason is the
underlying hardware, the cache monitor and memory bandwidth counters, are 64bit width.
Using 32bit interface to access these counters are problematic. This bug is not found because
this interface is only used for tracking the amount of cache that used before this patch, normally
the occupied cache will not exceed 4GB range. (32bit counter can counter value up to 4GB).
But for memory, this counter records the data passing through the memory controller issued
by this CPU in bytes and accumulatively, this value can easily exceed the 4GB bound, so I
don’t want to reserve the old 32 bit interface and let user use it, because it will report incorrect value.
We simply have to document the limitati onof the old interface. We can
*NOT* change it, because it WILL break API compatibility for apps that
deserailize the current data.


Got. I'll resend new patches for review.


Thanks

Huaqiang




Regards,
Daniel


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