From: Stephen Boyd <swboyd@chromium.org>
To: Andy Gross <agross@kernel.org>,
Bjorn Andersson <bjorn.andersson@linaro.org>,
Douglas Anderson <dianders@chromium.org>,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
rafael.j.wysocki@intel.com
Cc: mka@chromium.org, mkshah@codeaurora.org, evgreen@chromium.org,
Douglas Anderson <dianders@chromium.org>,
linux-arm-msm@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v4 5/5] soc: qcom: rpmh-rsc: Remove the pm_lock
Date: Thu, 23 Apr 2020 20:59:52 -0700 [thread overview]
Message-ID: <158770079266.135303.7831640949542355577@swboyd.mtv.corp.google.com> (raw)
In-Reply-To: <20200422145408.v4.5.I295cb72bc5334a2af80313cbe97cb5c9dcb1442c@changeid>
Quoting Douglas Anderson (2020-04-22 14:55:03)
> It has been postulated that the pm_lock is bad for performance because
> a CPU currently running rpmh_flush() could block other CPUs from
> coming out of idle. Similarly CPUs coming out of / going into idle
> all need to contend with each other for the spinlock just to update
> the variable tracking who's in PM.
>
> Let's optimize this a bit. Specifically:
>
> - Use a count rather than a bitmask. This is faster to access and
> also means we can use the atomic_inc_return() function to really
> detect who the last one to enter PM was.
> - Accept that it's OK if we race and are doing the flush (because we
> think we're last) while another CPU is coming out of idle. As long
> as we block that CPU if/when it tries to do an active-only transfer
> we're OK.
>
> Signed-off-by: Douglas Anderson <dianders@chromium.org>
> ---
Reviewed-by: Stephen Boyd <swboyd@chromium.org>
next prev parent reply other threads:[~2020-04-24 3:59 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-04-22 21:54 [PATCH v4 1/5] soc: qcom: rpmh-rsc: Corrently ignore CPU_CLUSTER_PM notifications Douglas Anderson
2020-04-22 21:55 ` [PATCH v4 2/5] soc: qcom: rpmh-rsc: We aren't notified of our own failure w/ NOTIFY_BAD Douglas Anderson
2020-04-23 4:48 ` Maulik Shah
2020-04-24 2:38 ` Stephen Boyd
2020-04-24 2:41 ` Stephen Boyd
2020-04-22 21:55 ` [PATCH v4 3/5] kernel/cpu_pm: Fix uninitted local in cpu_pm Douglas Anderson
2020-04-24 2:43 ` Stephen Boyd
2020-04-22 21:55 ` [PATCH v4 4/5] soc: qcom: rpmh-rsc: Simplify locking by eliminating the per-TCS lock Douglas Anderson
2020-04-24 2:48 ` Stephen Boyd
2020-04-24 16:47 ` Doug Anderson
2020-04-22 21:55 ` [PATCH v4 5/5] soc: qcom: rpmh-rsc: Remove the pm_lock Douglas Anderson
2020-04-24 3:59 ` Stephen Boyd [this message]
2020-04-23 4:45 ` [PATCH v4 1/5] soc: qcom: rpmh-rsc: Corrently ignore CPU_CLUSTER_PM notifications Maulik Shah
2020-04-23 16:19 ` Doug Anderson
2020-04-24 2:38 ` Stephen Boyd
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