From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 72626C6FA86 for ; Thu, 22 Sep 2022 10:53:00 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230475AbiIVKw7 (ORCPT ); Thu, 22 Sep 2022 06:52:59 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:52080 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230122AbiIVKw4 (ORCPT ); Thu, 22 Sep 2022 06:52:56 -0400 Received: from dfw.source.kernel.org (dfw.source.kernel.org [IPv6:2604:1380:4641:c500::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 10AEAD12CF for ; Thu, 22 Sep 2022 03:52:56 -0700 (PDT) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id A3B3B62C17 for ; Thu, 22 Sep 2022 10:52:55 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 5B825C433D6; Thu, 22 Sep 2022 10:52:52 +0000 (UTC) Date: Thu, 22 Sep 2022 11:52:48 +0100 From: Catalin Marinas To: James Clark Cc: coresight@lists.linaro.org, linux-arm-kernel@lists.infradead.org, suzuki.poulose@arm.com, mathieu.poirier@linaro.org, mike.leach@linaro.org, leo.yan@linaro.org, broonie@kernel.org, linux-kernel@vger.kernel.org, Will Deacon , Mark Rutland Subject: Re: [PATCH 0/1] arm64: defconfig: Add Coresight as module Message-ID: References: <20220921140535.152627-1-james.clark@arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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