Re: [PATCH v3 03/18] x86/tsc/paravirt: Remove the read_tsc and read_tscp paravirt hooks

Borislav Petkov
2015-06-19T15:32:16Z

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@kernel.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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