From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from relay.hostedemail.com (smtprelay0012.hostedemail.com [216.40.44.12]) (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 118CB31F9BE for ; Wed, 20 May 2026 16:52:11 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=216.40.44.12 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1779295933; cv=none; b=MR4OyJ5+mrSTIexRQq5E1dSZEYqIg75dLcAPNC/oPalrpPmPZuuqKKXbkIwe6fq+4I+eqsjc6IrzNzm3XnPCmwhc8Z7JLZLrIUPV0RFO2vhZyQ0yCOhog3naJ8SP/4TQMEiOXcG1rpmqn+n6TWSHUz3Og0LLi+1rkemLEgi7rPA= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1779295933; c=relaxed/simple; bh=KcjqQxuc4JaQGnGOdcE2k3Aakq+W6rdjrYaXiDlJfRQ=; h=Date:From:To:Cc:Subject:Message-ID:In-Reply-To:References: MIME-Version:Content-Type; b=u+/oE1mkBYD4d+1Z97H2iBXKioiZIC1IWFqxVIm0842tB0yWa0pTT8UQJd1ze+Xplbb9C18Jjvihtg25iSauPr4oZJV5BdklilUlVaCVRINZReuCNSKAsgml/pUKCo82juT7294hC5DSz5CyX+OI+GwsgYMxUIpFxRCgUxZL1Lo= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=goodmis.org; spf=pass smtp.mailfrom=goodmis.org; arc=none smtp.client-ip=216.40.44.12 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=goodmis.org Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=goodmis.org Received: from omf11.hostedemail.com (lb01a-stub [10.200.18.249]) by unirelay03.hostedemail.com (Postfix) with ESMTP id CDA68A03D0; Wed, 20 May 2026 16:52:09 +0000 (UTC) Received: from [HIDDEN] (Authenticated sender: rostedt@goodmis.org) by omf11.hostedemail.com (Postfix) with ESMTPA id 69DD42002C; Wed, 20 May 2026 16:52:07 +0000 (UTC) Date: Wed, 20 May 2026 12:52:26 -0400 From: Steven Rostedt To: Shrikanth Hegde Cc: Valentin Schneider , LKML , Peter Zijlstra , Tejun Heo , Juri Lelli , Vincent Guittot , Dietmar Eggemann , Ben Segall , Mel Gorman , K Prateek Nayak , Kyle McMartin Subject: Re: [PATCH v2] sched/rt: Have RT_PUSH_IPI be default off for non PREEMPT_RT Message-ID: <20260520125226.50b83e76@gandalf.local.home> In-Reply-To: <61203cdb-af98-47e6-bb70-78af7f0f1cbc@linux.ibm.com> References: <20260515103740.25ccbed8@gandalf.local.home> <61203cdb-af98-47e6-bb70-78af7f0f1cbc@linux.ibm.com> X-Mailer: Claws Mail 3.20.0git84 (GTK+ 2.24.33; x86_64-pc-linux-gnu) 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-Transfer-Encoding: 7bit X-Rspamd-Queue-Id: 69DD42002C X-Rspamd-Server: rspamout06 X-Stat-Signature: 7yeoh61u467by55f8fwoxtoa7wcj81eq X-Session-Marker: 726F737465647440676F6F646D69732E6F7267 X-Session-ID: U2FsdGVkX19hTuhlFIkIruJboV3dy6cEx8lK4ve/8PM= X-HE-Tag: 1779295927-674750 X-HE-Meta: U2FsdGVkX1+Y1KMEwQTximNaq9yQ1uassQ9aevhG4pbD9jrQ3DB4c6N6EHKIuDhnJtXOx07erKcFYOauQkypuC3b0qrBGszruL/Syry+KKYsjfeCzeyv/aeWW2DUzkFULvACYKDm+Xfd/RyfN2NSy5ssSIcow2Hv4bnKgPo/roLTjptyrXG+r0LyLj3E9d76uANKUhslUVzguR24CjEbzaQQOxF7sULe4as+RAOfMcvCNlGreuvWGxfkaCeV0vHpgFaC6rHz7YXTgth1AgQGKM/8QejbCZznhEeQosuvwE7EVd8e+jz3OjTEKC7dfYWpBPjtIZOY6ZzWXf/klc6crzjWY8VvLuBm On Wed, 20 May 2026 12:03:37 +0530 Shrikanth Hegde wrote: > On 5/18/26 2:17 PM, Valentin Schneider wrote: > > On 15/05/26 10:37, Steven Rostedt wrote: > > > I got a bit confused here, please correct me if I didn't get this right: > > > > Per handle_softirqs(), we can't restart the softirq handling loop if > > need_resched() is true (which would be the case here, per what we'd have > > done it push_rt_task(@pull=true)). > > I thought this meant softirqs couldn't be the issue, however this is only > > valid within the scope of a single handle_softirqs() invocation. > > > > AIUI here we're being hammered by IRQs, thus under this sort of pattern: > > > > > > __irq_exit_rcu() > > invoke_softirq() > > handle_softirqs() > > // handle NET_RX_SOFTIRQ > > // need_resched() is true so don't loop > > > > > > Wouldn't IRQ exit call schedule if need_resched is set? via irqentry_exit_cond_resched ? I haven't looked at the networking code, but does NAPI just continue looping while there are packets to process? Or is there a check if need_resched() is set, that it will exit out early? Yeah, I'm still wondering why this causes a live lock. -- Steve > > > // Barely any progress made here towards actually executing __schedule() > > > > > > __irq_exit_rcu() > > invoke_softirq() > > handle_softirqs() > > // handle NET_RX_SOFTIRQ and wake up some tasks > > // need_resched() is true so don't loop > > > > > > & repeat ad nauseam. Did I get this right? > >