linux-kernel - Re: [PATCH v2] drm/i915: Replace kmap() with kmap_local

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Message-ID: <20230620180759.GA419158@sumitra.com>
Date:   Tue, 20 Jun 2023 11:07:59 -0700
From:   Sumitra Sharma <sumitraartsy@...il.com>
To:     Ira Weiny <ira.weiny@...el.com>
Cc:     Jani Nikula <jani.nikula@...ux.intel.com>,
        Joonas Lahtinen <joonas.lahtinen@...ux.intel.com>,
        Rodrigo Vivi <rodrigo.vivi@...el.com>,
        Tvrtko Ursulin <tvrtko.ursulin@...ux.intel.com>,
        David Airlie <airlied@...il.com>,
        Daniel Vetter <daniel@...ll.ch>,
        intel-gfx@...ts.freedesktop.org, dri-devel@...ts.freedesktop.org,
        linux-kernel@...r.kernel.org,
        Thomas Hellström (Intel) 
        <thomas_os@...pmail.org>, Fabio <fmdefrancesco@...il.com>,
        Deepak R Varma <drv@...lo.com>,
        Sumitra Sharma <sumitraartsy@...il.com>
Subject: Re: [PATCH v2] drm/i915: Replace kmap() with kmap_local_page()


On Tue, Jun 20, 2023 at 06:23:38AM -0700, Ira Weiny wrote:
> Sumitra Sharma wrote:
> > On Sun, Jun 18, 2023 at 11:11:08AM -0700, Ira Weiny wrote:
> > > Sumitra Sharma wrote:
> > > > kmap() has been deprecated in favor of the kmap_local_page()
> > > > due to high cost, restricted mapping space, the overhead of a
> > > > global lock for synchronization, and making the process sleep
> > > > in the absence of free slots.
> > > > 
> > > > kmap_local_page() is faster than kmap() and offers thread-local
> > > > and CPU-local mappings, take pagefaults in a local kmap region
> > > > and preserves preemption by saving the mappings of outgoing tasks
> > > > and restoring those of the incoming one during a context switch.
> > > > 
> > > > The mapping is kept thread local in the function
> > > > “i915_vma_coredump_create” in i915_gpu_error.c
> > > > 
> > > > Therefore, replace kmap() with kmap_local_page().
> > > > 
> > > > Suggested-by: Ira Weiny <ira.weiny@...el.com>
> > > > 
> > > 
> > > NIT: No need for the line break between Suggested-by and your signed off line.
> > > 
> > 
> > Hi Ira,
> > 
> > What does NIT stand for? 
> 
> Shorthand for 'nitpicking'.
> 
> "giving too much attention to details that are not important, especially
> as a way of criticizing: "
> 
> 	- https://dictionary.cambridge.org/dictionary/english/nitpicking
> 
> Via email this is a way for authors of an email to indicate something is
> technically wrong but while nicely acknowledging that it is not very
> significant and could be seen as overly critical.
> 
> For this particular comment I'm showing something to pay attention to next
> time but that was not a big deal this time around.
>

Hi Ira,

Thank for your explanation on NIT. 


> > 
> > Thank you. I will take care about the line breaks.
> > 
> > > > Signed-off-by: Sumitra Sharma <sumitraartsy@...il.com>
> > > > ---
> > > > 
> > > > Changes in v2:
> > > > 	- Replace kmap() with kmap_local_page().
> > > 
> > > Generally it is customary to attribute a change like this to those who
> > > suggested it in a V1 review.
> > > 
> > > For example:
> > > 
> > >  	- Tvrtko/Thomas: Use kmap_local_page() instead of page_address()
> > > 
> > > Also I don't see Thomas on the new email list.  Since he took the time to
> > > review V1 he might want to check this version out.  I've added him to the
> > > 'To:' list.
> > > 
> > > Also a link to V1 is nice.  B4 formats it like this:
> > > 
> > > - Link to v1: https://lore.kernel.org/all/20230614123556.GA381200@sumitra.com/
> > > 
> > > All that said the code looks good to me.  So with the above changes.
> > > 
> > > Reviewed-by: Ira Weiny <ira.weiny@...el.com>
> > > 
> > 
> > I have noted down the points mentioned above. Thank you again.
> > 
> > I am not supposed to create another version of this patch for 
> > adding the above mentions, as you and Thomas both gave this patch 
> > a reviewed-by tag. Right?
> > 
> 
> Based on this response[*] from Tvrtko I think this version can move
> through without a v3.

Okay!


Thanks & regards
Sumitra

> 
> Thanks!
> Ira
> 
> [*] https://lore.kernel.org/all/bcb0a1d2-cd4d-a56f-1ee6-7ccfdd2f7b38@linux.intel.com/
> 
> <quote>
> Thanks all! I'll just re-send the patch for our CI, since it didn't get
> picked up automatically (stuck in moderation perhaps), with all r-b tags
> added and extra line space removed and merge it if results will be green.
> 
> Regards,
> 
> Tvrtko
> </quote>
> 
> 
> > 
> > Thanks & regards
> > Sumitra
> > 
> > PS: I am new to the open source vocabulary terms.
> > 
> > > > 	- Change commit subject and message.
> > > > 
> > > >  drivers/gpu/drm/i915/i915_gpu_error.c | 4 ++--
> > > >  1 file changed, 2 insertions(+), 2 deletions(-)
> > > > 
> > > > diff --git a/drivers/gpu/drm/i915/i915_gpu_error.c b/drivers/gpu/drm/i915/i915_gpu_error.c
> > > > index f020c0086fbc..bc41500eedf5 100644
> > > > --- a/drivers/gpu/drm/i915/i915_gpu_error.c
> > > > +++ b/drivers/gpu/drm/i915/i915_gpu_error.c
> > > > @@ -1164,9 +1164,9 @@ i915_vma_coredump_create(const struct intel_gt *gt,
> > > >  
> > > >  			drm_clflush_pages(&page, 1);
> > > >  
> > > > -			s = kmap(page);
> > > > +			s = kmap_local_page(page);
> > > >  			ret = compress_page(compress, s, dst, false);
> > > > -			kunmap(page);
> > > > +			kunmap_local(s);
> > > >  
> > > >  			drm_clflush_pages(&page, 1);
> > > >  
> > > > -- 
> > > > 2.25.1
> > > > 
> > > 
> > > 
> 
>