Re: getting processor numbers

Eric Dumazet
2007-04-04T05:10:24Z

H. Peter Anvin a écrit :
> Jeremy Fitzhardinge wrote:
>> H. Peter Anvin wrote:
>>> Sounds like it would need a device which can be waited upon for changes.
>>
>> A vdso-like shared page could have a futex in it.
>
> Yes, but a futex couldn't be waited upon with a bunch of other things as
> part of a poll or a select. The cost of reading the information is
> minimal.
>

There is one thing that always worried me.

Intel & AMD manuals make clear that mixing data and program in the same page
is bad for performance.

In particular, x86_64 vsyscall put jiffies and other vsyscall_gtod_data_t
right in the midle of code. That is certainly not wise.

A probably sane implementation should use two pages, one for code, one for data.