From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from desiato.infradead.org (desiato.infradead.org [90.155.92.199]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id E38D12DE701 for ; Fri, 6 Feb 2026 09:47:21 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=90.155.92.199 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1770371242; cv=none; b=oZLSh7Iczl9BbeY8n8xTpNuRQ24BiR7Qv0y+QVC8lDvIo/aquEREwik8dccHi3Zu4lmICwywrV4fJle6czuDwMD1OxpraV5sNRUdKRRdVb93Ag4URJQA9jGuB3AJarpHFvIB1KS/EHu4PbQQT3aDOQNkPaxYRzoplTqr42m90Aw= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1770371242; c=relaxed/simple; bh=+MuOqXNfTkStoCH2sBMTvenVLlAIefe/XR811WFtGRo=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=H83BEplW36VDnU00lABOCu9Ny23O+mp6FhPbFS3N5o4nSR86IRJZnGJCKE0LLf+IUPkh1lpHaK/PKiiMaWOCXANGJf2HHatoVQM2HmVcDGb1Hl08/4vzcmimBopFQTPD5FUUqR1ziWevpYfKLA5HaOw6JlS5zbHTahQL5HAHHKs= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=infradead.org; spf=none smtp.mailfrom=infradead.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b=Jm4/TmkI; arc=none smtp.client-ip=90.155.92.199 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=infradead.org Authentication-Results: smtp.subspace.kernel.org; spf=none smtp.mailfrom=infradead.org Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="Jm4/TmkI" DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=desiato.20200630; h=In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=GrpKXtzyVfKqHUaE2ZRQNbmC7wcwBmWUTerg+iAVzGk=; b=Jm4/TmkIDmr3zAH0e60YxY6XQD RTUeLlFfgmYgFs2X2Vo7IukNge1cgHpmmdeIM1iuQtw5jpo6QZn30eI463ZXMMc2f067sJk/MjiPB ncAcHGhaW7ePCekDwulpaQCexForLlN7tSlA+w/9qNcP6/jTHTHcZCetkD8IOowIKZlbDHghsTNSG 1sY/5YSK3sizAe4wlxBVThe8H/CvMzdDTWGo8shAs0GN70yVk3r/6qOZTfnCJPkfu8Gd0aTfWp5gG 69kCMjdYRXA3u6ZAq4UbLnlnv7bdxd9ghnZwhbtJWe4JJyRUWF2Io/zUJMjRfKhRiNJ9BAGwuYw0+ s5bc7WoA==; Received: from 77-249-17-252.cable.dynamic.v4.ziggo.nl ([77.249.17.252] helo=noisy.programming.kicks-ass.net) by desiato.infradead.org with esmtpsa (Exim 4.98.2 #2 (Red Hat Linux)) id 1voIQc-00000003ZiW-2clV; Fri, 06 Feb 2026 09:47:09 +0000 Received: by noisy.programming.kicks-ass.net (Postfix, from userid 1000) id 5D5E0302DA9; Fri, 06 Feb 2026 10:47:00 +0100 (CET) Date: Fri, 6 Feb 2026 10:47:00 +0100 From: Peter Zijlstra To: Chuyi Zhou Cc: tglx@linutronix.de, mingo@redhat.com, luto@kernel.org, paulmck@kernel.org, muchun.song@linux.dev, bp@alien8.de, dave.hansen@linux.intel.com, linux-kernel@vger.kernel.org Subject: Re: [PATCH 05/11] smp: Enable preemption early in smp_call_function_many_cond Message-ID: <20260206094700.GR1282955@noisy.programming.kicks-ass.net> References: <20260203112401.3889029-1-zhouchuyi@bytedance.com> <20260203112401.3889029-6-zhouchuyi@bytedance.com> <20260205095236.GI232055@noisy.programming.kicks-ass.net> <20260205105704.GA245049@noisy.programming.kicks-ass.net> <261ae19f-e3d1-4017-be1e-90b5c6d91dc7@bytedance.com> <20260205145912.GM2995752@noisy.programming.kicks-ass.net> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: On Fri, Feb 06, 2026 at 04:43:48PM +0800, Chuyi Zhou wrote: > However, 99% of callers have preemption disabled, some of them even > invoking it within spin_locks (for example, we might trigger a TLB flush > while holding pte spinlocks). Then 99% of the callers don't benefit from this and won't see your latency reduction -- and will be broken on PREEMPT_RT, no?