From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Subject: Re: [RFC PATCH] powerpc: enable cpu clock for powerpc64 References: <1449208206.30683.9.camel@TP420> From: Jens Axboe Message-ID: <5661CC63.7070305@kernel.dk> Date: Fri, 4 Dec 2015 10:24:51 -0700 MIME-Version: 1.0 In-Reply-To: <1449208206.30683.9.camel@TP420> Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit To: Li Zhong , fio@vger.kernel.org List-ID: On 12/03/2015 10:50 PM, Li Zhong wrote: > This patch tries to enable cpu clock for powerpc64, the code is copied from > mftb() in kernel source. > > The two instructions after mfspr are added in the kernel to solve an erratum on > Cell and fsl booke CPUs. On those CPUs, 64 bits mftb is not atomic, so it is > possible that the low order 32 bits are already reset to 0x00000000 but the > high order bits are not yet incremented by one. > > Don't know how to tell whether it will be running on those CPUs or not, I just > keep the above fix for all ppc64 CPUs. Even if we have some method to check > whether we are on those CPUs or not at run time, I think the check won't cost > less than the two added instructions. Maybe we could use the similar fix up > code kernel uses to dynamically patch the instructions with nops if not needed. > But that would add much more complexity. Thanks, applied. I don't have any powerpc hw, so I'll depend on your testing for this. -- Jens Axboe