From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from galois.linutronix.de (Galois.linutronix.de [193.142.43.55]) (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 B7808388869 for ; Thu, 3 Sep 2026 16:03:20 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=193.142.43.55 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1788451402; cv=none; b=IU/ywHzE46y2S/G4pUgOBah440uqJuy4dmwERtU1LKJeuMzFK2n6Y/eaQagYFljXK4fcrVNXHvPtI+0Fxs4pYkdsqA+7WMpNG6PxGXkFlBtQVk5Je8VwT3mBsbmg56ItI6gWTGktf/9lFYN2D51olkvy5TfZGG9Tv59ctzpp1Jg= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1788451402; c=relaxed/simple; bh=qMT1NX+zIHgJmJlgodutkDLJfbNg/gbC5a0twUCi6TA=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=hKxUFfCHCm4KJhBQeKWFuJ/i/RGcNLGW8zS6P/GCoZETRtLfpWjh5lyiNi1q8ZWJv3H0nNWq6c/DCDx64I2Zzz+X2NSM+eiGf3Y+nwsG9bpM/ES6MOGwZgBuuXU0IkKyz319px0Vdcx9jMrhqTqhd9UFeBx/FSMMTgH0h7p0Qo4= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linutronix.de; spf=pass smtp.mailfrom=linutronix.de; dkim=pass (2048-bit key) header.d=linutronix.de header.i=@linutronix.de header.b=OOEvCkAm; dkim=permerror (0-bit key) header.d=linutronix.de header.i=@linutronix.de header.b=ikuJDRHT; arc=none smtp.client-ip=193.142.43.55 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linutronix.de Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linutronix.de Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=linutronix.de header.i=@linutronix.de header.b="OOEvCkAm"; dkim=permerror (0-bit key) header.d=linutronix.de header.i=@linutronix.de header.b="ikuJDRHT" Date: Thu, 3 Sep 2026 18:03:17 +0200 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020; t=1788451398; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=LjgTxkB5zSVJzJcaPywHI0T0gYLDigFmAh14plXp34M=; b=OOEvCkAmwFpas5OUKiujIY3hbBzn4shpq83enDwyRsZr55zouKLf9Cnv9ugfNVua/su6pc zg99uLiLi1xy0BV9WLaAxhB5UfogQWmlZ0CgEmxLmwhfCsb0kJd6hkdcV17nv88L72SjJS PMxVBq5yDvs0zs4R0FXRMamxINJDib/AUkS1U0k+/RvldhE2oQlI8J2haTf+GRAx37QKKI mHOXVouoLgxor52J6iAvAcM1ZD3Oz2wZKi2di8EYP7F6hwKhujc/jVVm1OtiV7XA0YvRtD 9qbmYJ4O5dvitGqrXbIpNycx7nZxtQS7c4tdzVMnxH3C13jRS6nVsIcBPCtocg== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1788451398; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=LjgTxkB5zSVJzJcaPywHI0T0gYLDigFmAh14plXp34M=; b=ikuJDRHTsO3XeJJYqCQfqsThXrmxlh2Dz2nbRv2Wunm7MQb5gwMfCAZX+fpzVFslICRqMS 9G7UN4A/Tim8eRDw== From: Sebastian Andrzej Siewior To: Nikita Taranov Cc: Thomas Gleixner , Ingo Molnar , Peter Zijlstra , Darren Hart , Davidlohr Bueso , =?utf-8?B?QW5kcsOp?= Almeida , linux-kernel@vger.kernel.org, regressions@lists.linux.dev Subject: Re: futex: private hash can stay on the shared atomic refcount indefinitely after auto-scaling Message-ID: <20260903160317.-6L7VXXK@linutronix.de> References: <20260823150046.204417-1-nickita.taranov@gmail.com> <20260824160337.0IvfKx8A@linutronix.de> <20260825170605.2462933-1-nickita.taranov@gmail.com> <20260901230559.1978876-1-nickita.taranov@gmail.com> <20260902075604.A_-jz823@linutronix.de> <20260902213143.3426531-1-nickita.taranov@gmail.com> 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=utf-8 Content-Disposition: inline In-Reply-To: <20260902213143.3426531-1-nickita.taranov@gmail.com> On 2026-09-02 21:31:42 [+0000], Nikita Taranov wrote: > The problem was originally observed on a synthetic benchmark that pretty much > did what the first repro does. On that benchmark, it was really bad as you saw. > I've never seen it on a real workload, so cannot comment on that. Okay. In that case I need to figure if we want to care about a regression on micro benchmark. > stock v7.3-rc1 + your patch > Xeon 6975P-C 96c/192t 8/8 at 96,128,192 0/8 everywhere > Graviton4 Neoverse-V2 see below 0/8 everywhere > AMD EPYC 9R45 0/8 (never stalls) 0/8 So this means my quick hacked fixed your problem? > I'm guessing your patch was an early stage draft, but just in case let me flag > one problem I saw: on the Intel box the futex selftests regress: > > stock v7.3-rc1 14 passed, 0 failed > + your patch 12 passed, 2 failed > > futex_requeue requeue_multiple: > expected 10 == futex_cmp_requeue(f1, 0, &f2, 3, 7, 0), got 0 > expected 7 == futex_wake(&f2, INT_MAX, 0), got 0 > futex_requeue_pi 2 of 24 fail: broadcast_owner, owner > "Test terminated by timeout" Yeah, I might have got something wrong. It was just an idea but might look into this if we need this fixed. Thanks for the feedback. > Regards. Sebastian