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From:   Thomas Gleixner <tglx@linutronix.de>
To:     ira.weiny@intel.com, Ingo Molnar <mingo@redhat.com>,
        Borislav Petkov <bp@alien8.de>,
        Andy Lutomirski <luto@kernel.org>,
        Peter Zijlstra <peterz@infradead.org>,
        Dave Hansen <dave.hansen@linux.intel.com>
Cc:     Ira Weiny <ira.weiny@intel.com>, x86@kernel.org,
        linux-kernel@vger.kernel.org,
        Andrew Morton <akpm@linux-foundation.org>,
        Fenghua Yu <fenghua.yu@intel.com>, linux-doc@vger.kernel.org,
        linux-nvdimm@lists.01.org, linux-mm@kvack.org,
        linux-kselftest@vger.kernel.org,
        Dan Williams <dan.j.williams@intel.com>,
        Greg KH <gregkh@linuxfoundation.org>
Subject: Re: [PATCH V3 05/10] x86/entry: Pass irqentry_state_t by reference
In-Reply-To: <20201106232908.364581-6-ira.weiny@intel.com>
References: <20201106232908.364581-1-ira.weiny@intel.com> <20201106232908.364581-6-ira.weiny@intel.com>
Date:   Sun, 15 Nov 2020 19:58:52 +0100
Message-ID: <87mtzi8n0z.fsf@nanos.tec.linutronix.de>
MIME-Version: 1.0
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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.

> 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?

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?

Thanks

        tglx