linux-kernel - Re: [PATCH 2/2] powerpc: implement arch_scale_smt

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <4B577F1A.9060907@austin.ibm.com>
Date:	Wed, 20 Jan 2010 16:09:30 -0600
From:	Joel Schopp <jschopp@...tin.ibm.com>
To:	Michael Neuling <mikey@...ling.org>
CC:	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Ingo Molnar <mingo@...e.hu>, linuxppc-dev@...ts.ozlabs.org,
	linux-kernel@...r.kernel.org, ego@...ibm.com
Subject: Re: [PATCH 2/2] powerpc: implement arch_scale_smt_power for Power7


>> +	if (cpu_has_feature(CPU_FTRS_POWER7) && weight == 4) {
>>     
>
> I think we should avoid using cpu_has_feature like this.  It's better to
> create a new feature and add it to POWER7 in the cputable, then check
> for that here.
>
> The way that it is now, I think any CPU that has superset of the POWER7
> features, will be true here.  This is not what we want.
>   
Any ideas for what to call this feature?  ASYM_SMT4 ?
>
>> +	smt_gain /= weight;
>>     
>
> This results in a PPC div, when most of the time it's going to be a
> power of two divide.  You've optimised the divides a few lines above
> this, but not this one.  Some consistency would be good.
>
>   
I can turn that into a conditional branch (case statement) with a shift 
for the common 1,2,4 cases which should cover all procs available today 
falling back to a divide for any theoretical future processors that do 
other numbers of threads.
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/