Re: Need some guidance working on a TODO item

Re: Need some guidance working on a TODO item

[Laurent Pinchart]

Hello Ghanshyam,

CC'ing the linux-media mailing list, to let other developers chime in as
well.

On Sat, Oct 28, 2023 at 04:07:03PM +0530, Ghanshyam Agrawal wrote:
> Hello Laurent,
> 
> Line 90 in file "drivers/media/usb/uvc/uvcvideo.h" in linux_mainline tree
> states
> 
> /*
>  * TODO: Put the most frequently accessed fields at the beginning of
>  * structures to maximize cache efficiency.
>  */
> 
> I am working on this todo item. Can you please guide me regarding 
> 
> 1. How can I find the number of accesses of each of the fields?

By reading through the code :-) It may be possible to instrument that,
but I have no idea how.

> 2. How can I find out the cache efficiency?

Do you know how caches work ?

> 3. When we say cache, which cache are we talking about?

The CPU caches, any level.

-- 
Regards,

Laurent Pinchart

Re: Need some guidance working on a TODO item

[Ghanshyam Agrawal]

On Tue, Oct 31, 2023 at 5:34 AM Laurent Pinchart
<laurent.pinchart@ideasonboard.com> wrote:
>
> Hello Ghanshyam,
>
> CC'ing the linux-media mailing list, to let other developers chime in as
> well.
>
> On Sat, Oct 28, 2023 at 04:07:03PM +0530, Ghanshyam Agrawal wrote:
> > Hello Laurent,
> >
> > Line 90 in file "drivers/media/usb/uvc/uvcvideo.h" in linux_mainline tree
> > states
> >
> > /*
> >  * TODO: Put the most frequently accessed fields at the beginning of
> >  * structures to maximize cache efficiency.
> >  */
> >
> > I am working on this todo item. Can you please guide me regarding
> >
> > 1. How can I find the number of accesses of each of the fields?
>
> By reading through the code :-) It may be possible to instrument that,
> but I have no idea how.
>
> > 2. How can I find out the cache efficiency?
>
> Do you know how caches work ?
>
> > 3. When we say cache, which cache are we talking about?
>
> The CPU caches, any level.
>
> --
> Regards,
>
> Laurent Pinchart

Hello Laurent,

Thanks for your email. I will read the code and figure out which
fields are accessed more frequently. I do have an understanding of the
caching mechanism; and as you mentioned "cpu caches", I will find out
the efficiency accordingly.

Thanks again. I appreciate your response.

Regards,
Ghanshyam Agrawal