Re: [Qemu-ppc] [PATCH 07/19] target/ppc: Make special ORs match x86 pause and don't generate on mttcg

[Cédric Le Goater]

On 2/13/19 5:54 AM, David Gibson wrote:
> On Wed, Feb 13, 2019 at 11:03:12AM +1100, Benjamin Herrenschmidt wrote:
>> On Tue, 2019-02-12 at 16:59 +1100, David Gibson wrote:
>>> On Mon, Jan 28, 2019 at 10:46:13AM +0100, Cédric Le Goater wrote:
>>>> From: Benjamin Herrenschmidt <address@hidden>
>>>>
>>>> There's no point in going out of translation on an SMT OR with
>>>> mttcg since the backend won't do anything useful such as pausing,
>>>> it's only useful on traditional TCG to give time to other
>>>> processors.
>>>
>>> Is it actively harmful in the MTTCG case, or just pointless?
>>
>> I think it can hurt performance, I don't remember for sure :)
>>
>>>> Signed-off-by: Benjamin Herrenschmidt <address@hidden>
>>>> Signed-off-by: Cédric Le Goater <address@hidden>
>>>> ---
>>>>  target/ppc/translate.c | 6 ++++--
>>>>  1 file changed, 4 insertions(+), 2 deletions(-)
>>>>
>>>> diff --git a/target/ppc/translate.c b/target/ppc/translate.c
>>>> index e169c43643a1..7d40a1fbe6bd 100644
>>>> --- a/target/ppc/translate.c
>>>> +++ b/target/ppc/translate.c
>>>> @@ -1580,7 +1580,7 @@ static void gen_pause(DisasContext *ctx)
>>>>      tcg_temp_free_i32(t0);
>>>>  
>>>>      /* Stop translation, this gives other CPUs a chance to run */
>>>> -    gen_exception_nip(ctx, EXCP_HLT, ctx->base.pc_next);
>>>> +    gen_exception_nip(ctx, EXCP_INTERRUPT, ctx->base.pc_next);
>>>
>>> I don't see how this change relates to the rest.
>>
>> Yeah not sure anymore :-)
> 
> Oh.  That certainly doesn't make this easier to review.
> 
> So, all these target/ppc patches are only indirectly related to XIVE
> pnv support.  Cédric, can you split them out into their own series on
> the next spin.

Sure. I will address your comments and resend them first.
 
Thanks,

C.

> 
>>
>>>>  }
>>>>  #endif /* defined(TARGET_PPC64) */
>>>>  
>>>> @@ -1662,7 +1662,9 @@ static void gen_or(DisasContext *ctx)
>>>>           * than no-op, e.g., miso(rs=26), yield(27), mdoio(29), mdoom(30),
>>>>           * and all currently undefined.
>>>>           */
>>>> -        gen_pause(ctx);
>>>> +        if (!mttcg_enabled) {
>>>> +            gen_pause(ctx);
>>>> +        }
>>>>  #endif
>>>>  #endif
>>>>      }
>>
>