linux-kernel - Re: [PATCH V3 05/10] x86/entry: Pass irqentry_state

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Message-ID: <20201116184916.GA722447@iweiny-DESK2.sc.intel.com>
Date:   Mon, 16 Nov 2020 10:49:16 -0800
From:   Ira Weiny <ira.weiny@...el.com>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Andy Lutomirski <luto@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
        linux-kernel@...r.kernel.org,
        Andrew Morton <akpm@...ux-foundation.org>,
        Fenghua Yu <fenghua.yu@...el.com>, linux-doc@...r.kernel.org,
        linux-nvdimm@...ts.01.org, linux-mm@...ck.org,
        linux-kselftest@...r.kernel.org,
        Dan Williams <dan.j.williams@...el.com>,
        Greg KH <gregkh@...uxfoundation.org>
Subject: Re: [PATCH V3 05/10] x86/entry: Pass irqentry_state_t by reference

On Sun, Nov 15, 2020 at 07:58:52PM +0100, Thomas Gleixner wrote:
> Ira,
> 
> On Fri, Nov 06 2020 at 15:29, ira weiny wrote:
> 
> Subject prefix wants to 'entry:'. This changes generic code and the x86
> part is just required to fix the generic code change.

Sorry, yes that was carried incorrectly from earlier versions.

> 
> > Currently struct irqentry_state_t only contains a single bool value
> > which makes passing it by value is reasonable.  However, future patches
> > propose to add information to this struct, for example the PKRS
> > register/thread state.
> >
> > Adding information to irqentry_state_t makes passing by value less
> > efficient.  Therefore, change the entry/exit calls to pass irq_state by
> > reference.
> 
> The PKRS muck needs to add an u32 to that struct. So how is that a
> problem?

There are more fields to be added for the kmap/pmem support.  So this will be
needed eventually.  Even though it is not strictly necessary in the next patch.

> 
> The resulting struct still fits into 64bit which is by far more
> efficiently passed by value than by reference. So which problem are you
> solving here?

I'm getting ahead of myself a bit.  I will be adding more fields for the
kmap/pmem tracking.

Would you accept just a clean up for the variable names in this patch?  I could
then add the pass by reference when I add the new fields later.  Or would an
update to the commit message be ok to land this now?

Ira

> 
> Thanks
> 
>         tglx
>