Re: [PATCH v4 2/2] add icswx support
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From: Tseng-Hui (Frank) Lin <hidden>
Date: 2011-03-04 23:07:37
On Sat, 2011-03-05 at 09:40 +1100, Benjamin Herrenschmidt wrote:
quoted
The lazy switching checks the shadow variable first before setting ACOP register. This saves mtspr() only if the new value is the same as current. If there are several coprocessors on the system, the ACOP register may have to be changed frequently. In that case, the lazy switching will not save time. In extreme case when the ACOP register needs to be changed every time, it actually slows down the execution by the additional shadow variable checking.By how much ? Is it even measurable ?
I don't have any measurable numbers. That's why I made it an option in case people wants to disable it. I do agree that the kernel has so many options that we should refrain from adding more. If the chance that the lazy switching slows down the execution is really low, we should just take out the option. Is there any one has an idea how much the numbers are?
Cheers, Ben. _______________________________________________ Linuxppc-dev mailing list Linuxppc-dev@lists.ozlabs.org https://lists.ozlabs.org/listinfo/linuxppc-dev