Re: Why is get_user_pages so slow?

[Micha Nelissen]

Hi Kevin,

Kevin Easton wrote:
> Yep, you are.  Because your pointer 'p' is a pointer to int, when you 
> increment it by 0x1000 in your loops you are actually incrementing it by 
> 0x1000 * sizeof(int) - so you're only actually touching one page in four.

Oops sorry, thanks for catching my mistake.

I also discovered the following: if I read from all pages, then call 
get_user_pages, it is still quite slow (did I get a read-only page?). 
However, if I touch all pages by writing to them, then get_user_pages 
becomes a factor 40 times faster or so.

All is clear now, I think. Thanks.

Micha
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/