linux-kernel - Re: [PATCH v3 03/18] x86/tsc/paravirt: Remove the read_tsc and read

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Message-ID: <20150619153201.GF12979@pd.tnic>
Date:	Fri, 19 Jun 2015 17:32:01 +0200
From:	Borislav Petkov <bp@...e.de>
To:	Andy Lutomirski <luto@...nel.org>
Cc:	x86@...nel.org, Peter Zijlstra <peterz@...radead.org>,
	John Stultz <john.stultz@...aro.org>,
	linux-kernel@...r.kernel.org, Len Brown <lenb@...nel.org>,
	Huang Rui <ray.huang@....com>,
	Denys Vlasenko <dvlasenk@...hat.com>, kvm@...r.kernel.org,
	Ralf Baechle <ralf@...ux-mips.org>
Subject: Re: [PATCH v3 03/18] x86/tsc/paravirt: Remove the read_tsc and
 read_tscp paravirt hooks

On Tue, Jun 16, 2015 at 05:35:51PM -0700, Andy Lutomirski wrote:
> We've had read_tsc and read_tscp paravirt hooks since the very
> beginning of paravirt, i.e., d3561b7fa0fb ("[PATCH] paravirt: header
> and stubs for paravirtualisation").  AFAICT the only paravirt guest
> implementation that ever replaced these calls was vmware, and it's
> gone.  Arguably even vmware shouldn't have hooked rdtsc -- we fully
> support systems that don't have a TSC at all, so there's no point
> for a paravirt implementation to pretend that we have a TSC but to
> replace it.
> 
> I also doubt that these hooks actually worked.  Calls to rdtscl and
> rdtscll, which respected the hooks, were used seemingly
> interchangeably with native_read_tsc, which did not.
> 
> Just remove them.  If anyone ever needs them again, they can try
> to make a case for why they need them.
> 
> Before, on a paravirt config:
>    text	   data	    bss	    dec	    hex	filename
> 13426505	1827056	14508032	29761593	1c62039	vmlinux
> 
> After:
>    text	   data	    bss	    dec	    hex	filename
> 13426617	1827056	14508032	29761705	1c620a9	vmlinux

Those look swapped. I mean, you're removing a bunch of stuff and text
grew?!

> Signed-off-by: Andy Lutomirski <luto@...nel.org>
> ---
>  arch/x86/include/asm/msr.h            | 16 ++++++++--------
>  arch/x86/include/asm/paravirt.h       | 34 ----------------------------------
>  arch/x86/include/asm/paravirt_types.h |  2 --
>  arch/x86/kernel/paravirt.c            |  2 --
>  arch/x86/kernel/paravirt_patch_32.c   |  2 --
>  arch/x86/xen/enlighten.c              |  3 ---
>  6 files changed, 8 insertions(+), 51 deletions(-)

-- 
Regards/Gruss,
    Boris.

ECO tip #101: Trim your mails when you reply.
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