From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp-relay-internal-1.canonical.com (smtp-relay-internal-1.canonical.com [185.125.188.123]) (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 8E86959B7E for ; Wed, 7 Feb 2024 15:13:02 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=185.125.188.123 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1707318785; cv=none; b=t3IQONkwpkvq2K9E2Cv/nPL37dC/cAFd30doxIyRnlLjTpgpZy24V18BfRpkLI1W5xfqqruQv4HQifLoam8HDn2U4dPBpVcyWLEpHWZzxkO9ZY8YARmtogvux1cLOreVvypT3MuuKG/RJjd3PHn0HnvSG3Sf1CM739dZVvJNc2A= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1707318785; c=relaxed/simple; bh=dqOwU8uND6czv3BzL1gYGmol8p0E71OBB7sTU6edAxc=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=TEpzGJgW18TszJxr2kAgCl3y5k8er7q1/L2g5d5LZs/ZYL1VA5rNORl1ZsQXkEcQRn9Ld81MlfVLfLxJgj98+EBySaDVckdCAN/iUWPCaTYdT/kjH4cyzmn7yM7JgrDnfHMH1XX2imPDgW/3iPhlsZggomtduOqveMTyRFi5qAc= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=canonical.com; spf=pass smtp.mailfrom=canonical.com; dkim=pass (2048-bit key) header.d=canonical.com header.i=@canonical.com header.b=DUjmkjv8; arc=none smtp.client-ip=185.125.188.123 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=canonical.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=canonical.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=canonical.com header.i=@canonical.com header.b="DUjmkjv8" Received: from mail-ed1-f70.google.com (mail-ed1-f70.google.com [209.85.208.70]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by smtp-relay-internal-1.canonical.com (Postfix) with ESMTPS id 8BFBB40606 for ; Wed, 7 Feb 2024 15:12:55 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=canonical.com; s=20210705; t=1707318775; bh=nDWokVGFpV3vHGNxZvMcm5ItVC5TKdedPzvIpgjtZp4=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:In-Reply-To; b=DUjmkjv8GY4w7zs02YyQjBhhz2pSsz9AqSX5GBCA9plQ23MlZ5iw4Z7/mnuk0g/zF 397K7kd+dkKWeBOpebQOwFMPumcnWPWZcxo/1ZDnyUhJ8El7ExvLEXHhibZf3gUEsI 7SFfTYY8kkWdwBageLW7qWuO6K5qqAHTyVvqzZP4cIyohOlw4Od3HSWjJ3mlLcFe7g qnFJwBo10oIycMk6Y0zL7nHBSlPP9m/OPBcvUEg56p0wiOMMsQRyWTd3i0zCt7j6cg pAgww8ARbjRs75HWGsZ52GzQgTDh1XNvBjza7ij1ZeDWu/l95mFF5WwHCfMYO2ESUw /0CKzkde4VgdQ== Received: by mail-ed1-f70.google.com with SMTP id 4fb4d7f45d1cf-558aafe9bf2so638196a12.1 for ; Wed, 07 Feb 2024 07:12:55 -0800 (PST) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1707318775; x=1707923575; h=in-reply-to:content-disposition:mime-version:references:message-id :subject:cc:to:from:date:x-gm-message-state:from:to:cc:subject:date :message-id:reply-to; bh=nDWokVGFpV3vHGNxZvMcm5ItVC5TKdedPzvIpgjtZp4=; b=mpEvHsadO2iSRN/NMq4icL1t6Il1MOpE/WQulBEg92UPKkzBQ0el11YSlyh1XKY8MK A2wW5Bk8zZaP2oTJJysL9DzRMOKsoCQwkOph8O1qL2hstpy7iDCs8N1WyuZc2Ul3t73r 58hUS1eavqQ96rk0+YaTxX64JL4V3ck6BGghiCiYL0UxLxWKe4RaSfxbFqKNvcUrLKb4 VoYSbgzEJRCF7VRZyepjtbr3a1TtB9pZzrXTzRdZ6LqLZ7IeMZ8qn1riApgZYmbQG6cI NyjS1ZoA98KRPLGuDtrdTyFTuZeNcpuyPpa+ocqol5Ij06sdJi+1KrqdlpGxprUaPzLb vrtA== X-Gm-Message-State: AOJu0YyThDGufORhUL0SyK2M8mH+vyplJ0ZHG6N6lsWGAwmL3WWG9eja 2FYwtclQwZQ7Vs2jo6HJZEjbWp6+mFUqK5u7fcnCjatAIk/ItaI/bXcHSHvIbPnmTPuZVwXSEQC 6vYDweR4MsaBodk82uRg3UMPjGzhkU3WKS1Vh/irLyBJah42djWUX+gydcA+dmgl8cw== X-Received: by 2002:a17:906:44c:b0:a38:8cc8:1197 with SMTP id e12-20020a170906044c00b00a388cc81197mr1115756eja.2.1707318775217; Wed, 07 Feb 2024 07:12:55 -0800 (PST) X-Google-Smtp-Source: AGHT+IHjUblLrm+tuJ5Sd4h+p8/GRkNYwbPAM72sH1xKUj82IyGS9HPdZx7buA5shOLQmPyLsr7l7A== X-Received: by 2002:a17:906:44c:b0:a38:8cc8:1197 with SMTP id e12-20020a170906044c00b00a388cc81197mr1115635eja.2.1707318772801; Wed, 07 Feb 2024 07:12:52 -0800 (PST) X-Forwarded-Encrypted: i=1; AJvYcCXQobeOPUpPTnddo/YGFKrQQNp5ew7uQWbDDlC8il+HXnslhJBQHEdiAu6NGZVBug6/VMG+FaCf2pO/ydQLL5PfI7lkgoeFQkuAwEwtkvSO7XukLtv30CK7xJQfpyvp77gOeQO40ykfyEodnLib071MWBTtDWZYGkt/h4zcGW+qfj1Z Received: from localhost (host-79-53-78-93.retail.telecomitalia.it. [79.53.78.93]) by smtp.gmail.com with ESMTPSA id ga25-20020a170906b85900b00a389490cb05sm306456ejb.29.2024.02.07.07.12.51 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 07 Feb 2024 07:12:52 -0800 (PST) Date: Wed, 7 Feb 2024 16:12:51 +0100 From: Andrea Righi To: Uladzislau Rezki Cc: "Paul E. McKenney" , Joel Fernandes , Joel Fernandes , rcu@vger.kernel.org, "Cc: Frederic Weisbecker" Subject: Re: Observation on NOHZ_FULL Message-ID: References: <6a2b6857-57e7-4321-adae-132ba69a4fff@paulmck-laptop> <0e15e91e-da47-45dd-b7de-7f89b7b6002b@joelfernandes.org> <92cba6df-01de-4daa-a0cb-5fa92c7374dd@paulmck-laptop> Precedence: bulk X-Mailing-List: rcu@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 Wed, Feb 07, 2024 at 02:04:12PM +0100, Uladzislau Rezki wrote: > > > > > > I repeated some tests in a more isolated environment and posted the > > > results here: > > > https://discourse.ubuntu.com/t/enable-low-latency-features-in-the-generic-ubuntu-kernel-for-24-04/42255 > > > > > > Highlights: > > > > > > - stress-ng --matrix seems quite unpredictable to be used a benchmarks > > > in this scenario (the bogo-ops/s are very susceptible to any kind of > > > interference, so even if in the long runs NO_HZ_FULL still seems to > > > provide some benefits looking at the average, we also need to > > > consider that there might be a significant error in the measurements, > > > standard deviation was pretty high) > > > > > > - fio doing short writes (in page cache) seems to perform like 2x > > > better in terms of iops with nohz_full, respect to the other cases > > > and it performs 2x slower with large IO writes (not sure why... need > > > to investigate more) > > > > > > - with lazy RCU enabled hrtimer_interrupt() takes like 2x more to > > > return, respect to the other cases (is this expected?) > > > > This last is surprising at first glance, but I could be missing > > something. Joel, Uladzislau, thoughts? > > > Could you please share the steps how you run "fio" tests? For short writes I was running something like this (on a 8 cores system): $ fio --rw=write --bs=1M --size=32M --numjobs=8 --name=worker --time_based --runtime=300 Larger writes: $ fio --rw=write --bs=1M --size=1G --numjobs=8 --name=worker --time_based --runtime=300 Thanks, -Andrea