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Subject: Re: [PATCH v4 6/9] x86: prevent inline distortion by paravirt ops
To:     Nadav Amit <namit@vmware.com>, linux-kernel@vger.kernel.org,
        x86@kernel.org
Cc:     Alok Kataria <akataria@vmware.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>,
        "H. Peter Anvin" <hpa@zytor.com>,
        virtualization@lists.linux-foundation.org
References: <20180612115050.185112-1-namit@vmware.com>
 <20180612115050.185112-7-namit@vmware.com>
From:   Juergen Gross <jgross@suse.com>
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Date:   Tue, 19 Jun 2018 17:09:22 +0200
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On 12/06/18 13:50, Nadav Amit wrote:
> GCC considers the number of statements in inlined assembly blocks,
> according to new-lines and semicolons, as an indication to the cost of
> the block in time and space. This data is distorted by the kernel code,
> which puts information in alternative sections. As a result, the
> compiler may perform incorrect inlining and branch optimizations.
> 
> The solution is to set an assembly macro and call it from the inlined
> assembly block. As a result GCC considers the inline assembly block as
> a single instruction.
> 
> The effect of the patch is a more aggressive inlining, which also
> causes a size increase of kernel.
> 
>    text	   data	    bss	    dec	    hex	filename
> 18147336 10226688 2957312 31331336 1de1408 ./vmlinux before
> 18162555 10226288 2957312 31346155 1de4deb ./vmlinux after (+14819)
> 
> Static text symbols:
> Before:	40053
> After:	39942	(-111)
> 
> Cc: Juergen Gross <jgross@suse.com>
> Cc: Alok Kataria <akataria@vmware.com>
> Cc: Thomas Gleixner <tglx@linutronix.de>
> Cc: Ingo Molnar <mingo@redhat.com>
> Cc: "H. Peter Anvin" <hpa@zytor.com>
> Cc: x86@kernel.org
> Cc: virtualization@lists.linux-foundation.org
> 
> Signed-off-by: Nadav Amit <namit@vmware.com>

Reviewed-by: Juergen Gross <jgross@suse.com>


Juergen