Re: [PATCH net-next 2/2] net: avoid calling sched_clock when LLSis off

[Eliezer Tamir]

On 28/06/2013 17:38, Andi Kleen wrote:
> > diff --git a/fs/select.c b/fs/select.c
> > index 79b876e..3654075 100644
> > --- a/fs/select.c
> > +++ b/fs/select.c
> > @@ -402,7 +402,7 @@ int do_select(int n, fd_set_bits *fds, struct timespec *end_time)
> >   	poll_table *wait;
> >   	int retval, i, timed_out = 0;
> >   	unsigned long slack = 0;
> > -	unsigned int ll_flag = POLL_LL;
> > +	unsigned int ll_flag = ll_get_flag();
>
> Is that a global flag? That's still the wrong level. It should
> look at something in the file descriptor (preferably without
> fetching any new cache lines)

There is a global flag that decides if we even try to find supported
files (sockets).

If it is on we look to see if anyone will return POLL_LL.
at the individual socket level, you need both the socket option to
be on, and the queue data to be available for it to return POLL_LL.

I wanted to find a way to control this at the time the user calls poll().
I was not able to find any simple way of doing it that way.
I'm open to suggestion.
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