Re: [PATCH v2 net-next] softirq: reduce latencies

Eric Dumazet
2013-01-04T17:00:28Z

On Fri, 2013-01-04 at 01:12 -0800, Joe Perches wrote:
> On Fri, 2013-01-04 at 00:23 -0800, Eric Dumazet wrote:
> > On Fri, 2013-01-04 at 00:15 -0800, Joe Perches wrote:
> > > Perhaps MAX_SOFTIRQ_TIME should be
> > > #define MAX_SOFTIRQ_TIME msecs_to_jiffies(2)
> > > though it would be nicer if it were a compile time constant.
> >
> > If you send a patch to convert msecs_to_jiffies() to an inline function
> > when HZ = 1000, I will gladly use it instead of (2*HZ/1000)
> >
> > Right now, max(1, msecs_to_jiffies(2)) uses way too many instructions,
> > while it should be the constant 2, known at compile time.
>
> Something like this might work.
>
> This is incomplete, it just does msecs_to_jiffies,
> and it should convert usecs_to_jiffies and the
> jiffies_to_<foo> types too.
>
> Maybe it's worthwhile.
>
> It does reduce object size by 16 bytes per call site
> (x86-32) when the argument is a constant. There are
> about 800 of these jiffies conversions in kernel sources.
>
> What do you think?
>

I think this is something to discuss in another thread, and definitely
worth to do, at least for msecs_to_jiffies()

We have many HZ references everywhere that could be cleaned up using
this.