From owner-freebsd-arch@FreeBSD.ORG Sat Apr 25 17:37:41 2015 Return-Path: Delivered-To: freebsd-arch@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [8.8.178.115]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by hub.freebsd.org (Postfix) with ESMTPS id B2BF8E30; Sat, 25 Apr 2015 17:37:41 +0000 (UTC) Received: from mail-ig0-x230.google.com (mail-ig0-x230.google.com [IPv6:2607:f8b0:4001:c05::230]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (Client CN "smtp.gmail.com", Issuer "Google Internet Authority G2" (verified OK)) by mx1.freebsd.org (Postfix) with ESMTPS id 7CE371766; Sat, 25 Apr 2015 17:37:41 +0000 (UTC) Received: by igbpi8 with SMTP id pi8so46004550igb.0; Sat, 25 Apr 2015 10:37:41 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20120113; h=mime-version:sender:in-reply-to:references:date:message-id:subject :from:to:cc:content-type; bh=Phb/NQoXTkr9L15luDeyDMGmHX6GVt6+Cca+aMGtFik=; b=BW1PBGeSmAO0UxLJtjFQkWYWilcq58ZJ1xgNqJ60O7nAMh0T55Ylt+sfIdhCRYuH2d kVbBmFrk9tv6I0mAzQZ+Dpi02rtdzTz/NdH222DpeVLcJMML0g+Dgc7atyq87s0/M6lO Bi47DERk7vYyxxxJE03dL+Mcx/JbHw5O/rVyeDywO7XepC6SluFmPF6zjTYDVcU25H6m RF9cN1dZ19jIhuBD/cI0Kb4enrKMi4i5Z3oRb2qRCp9AcuTOGeYTa5qGnKYxXtnIfBbn oUghd37pOwg3lAbCOPtZl0CmWlIVQ3DY+ceAe2oXL/j/heWbS83fP0Us5UT8W2ypGQqi lzzg== MIME-Version: 1.0 X-Received: by 10.50.141.198 with SMTP id rq6mr370239igb.6.1429983460954; Sat, 25 Apr 2015 10:37:40 -0700 (PDT) Sender: adrian.chadd@gmail.com Received: by 10.36.38.133 with HTTP; Sat, 25 Apr 2015 10:37:40 -0700 (PDT) In-Reply-To: References: Date: Sat, 25 Apr 2015 10:37:40 -0700 X-Google-Sender-Auth: DL0iYIbYI4Qj7SHIPjRU1Ltqndo Message-ID: Subject: Re: RFC: setting performance_cx_lowest=C2 in -HEAD to avoid lock contention on many-CPU boxes From: Adrian Chadd To: "K. Macy" Cc: "freebsd-arch@freebsd.org" Content-Type: text/plain; charset=UTF-8 X-BeenThere: freebsd-arch@freebsd.org X-Mailman-Version: 2.1.20 Precedence: list List-Id: Discussion related to FreeBSD architecture List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Sat, 25 Apr 2015 17:37:41 -0000 On 25 April 2015 at 10:18, K. Macy wrote: > Perhaps use an arbitrary cutoff - say <= 8 cores - where the > cx_lowest=C3. This serialization isn't going to hurt on systems with > more modest core counts. Maybe. I bet it's a function of the idle state entry rate and core count - so maybe at 8 cores it'll hurt but only if it's entering idle at a high rate. Eg, if it's taking a hell of a lot of interrupts but not maxing out the CPU. -adrian