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Date: Thu, 22 Sep 2022 11:52:48 +0100 From: Catalin Marinas <catalin.marinas@....com> To: James Clark <james.clark@....com> Cc: coresight@...ts.linaro.org, linux-arm-kernel@...ts.infradead.org, suzuki.poulose@....com, mathieu.poirier@...aro.org, mike.leach@...aro.org, leo.yan@...aro.org, broonie@...nel.org, linux-kernel@...r.kernel.org, Will Deacon <will@...nel.org>, Mark Rutland <mark.rutland@....com> Subject: Re: [PATCH 0/1] arm64: defconfig: Add Coresight as module On Thu, Sep 22, 2022 at 10:34:45AM +0100, James Clark wrote: > On 21/09/2022 16:08, Catalin Marinas wrote: > > 2. Always on CONFIG_PID_IN_CONTEXTIDR (we might as well remove the > > Kconfig entry). This would write the root pid namespace value > > (task_pid_nr()). > > If we're not worried about the overhead after all, this would be the > easiest solution. And then SPE or Coresight already decide whether they > want to use the value or not, so no further changes are needed. > > From Leo's patch there is a table that shows a 1% overhead with it > enabled permanently, and I've heard a figure like that mentioned before. > So I could also resurrect that patch to use static keys? Although it's a > bit more complicated, that would be my preference. And then we can have > that mode always on. I don't think we should bother with static keys, just always enable it but try to reduce/group the ISBs from all the functions called on the __switch_to() path. We may actually get a speed-up. -- Catalin
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