Re: [Xen-devel] [PATCH 3 of 5] rombios/ata: Reading this status register has no relevant side effects

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 26/11/12 16:51, Ian Campbell wrote:
> No relevant side effects according to some spec or according to the
> current qemu implementation?
>
> Does it have any "irrelevant" side effects?

I am not sure whether the spec gurarentees no side effects, but this is
according to the qemu implementation.  The codepath has no side effects
we could determine.

~Andrew

>
> On Mon, 2012-11-26 at 16:41 +0000, Andrew Cooper wrote:
>> So taking two traps when one will do is pointless.  This codepath is on the 
>> int
>> 0x13 hot path, and removing it has about a 30% reduction in the number of 
>> traps
>> to Qemu during Win7 boot.
>>
>> Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
>>
>> diff -r c223c044afbf -r a8645d836a0e tools/firmware/rombios/rombios.c
>> --- a/tools/firmware/rombios/rombios.c
>> +++ b/tools/firmware/rombios/rombios.c
>> @@ -2540,7 +2540,6 @@ static int await_ide(when_done,base,time
>>    Bit32u time=0,last=0;
>>    Bit16u status;
>>    Bit8u result;
>> -  status = inb(base + ATA_CB_STAT); // for the times you're supposed to 
>> throw one away
>>    for(;;) {
>>      status = inb(base+ATA_CB_STAT);
>>      time++;
>>
>> _______________________________________________
>> Xen-devel mailing list
>> Xen-devel@xxxxxxxxxxxxx
>> http://lists.xen.org/xen-devel
>

-- 
Andrew Cooper - Dom0 Kernel Engineer, Citrix XenServer
T: +44 (0)1223 225 900, http://www.citrix.com


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