From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from e06smtp13.uk.ibm.com (e06smtp13.uk.ibm.com [195.75.94.109]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (Client CN "e06smtp13.uk.ibm.com", Issuer "GeoTrust SSL CA" (not verified)) by ozlabs.org (Postfix) with ESMTPS id 7E1D22C009E for ; Wed, 11 Dec 2013 21:28:41 +1100 (EST) Received: from /spool/local by e06smtp13.uk.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Wed, 11 Dec 2013 10:28:37 -0000 Message-ID: <52A83EBE.4060305@linux.vnet.ibm.com> Date: Wed, 11 Dec 2013 11:30:22 +0100 From: Philippe Bergheaud MIME-Version: 1.0 To: Benjamin Herrenschmidt Subject: Re: [PATCH] powerpc: set default kernel thread priority to medium-low References: <1386661163-4478-1-git-send-email-felix@linux.vnet.ibm.com> <1386743357.27999.1.camel@concordia> <1386755340.15730.11.camel@pasglop> In-Reply-To: <1386755340.15730.11.camel@pasglop> Content-Type: text/plain; charset=us-ascii; format=flowed Cc: Linuxppc-dev@lists.ozlabs.org List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Benjamin Herrenschmidt wrote: > On Wed, 2013-12-11 at 17:29 +1100, Michael Ellerman wrote: > > >>It would be nice if you could make an assertion about what the state of HMT >>handling should be once your patch is applied. >> >>I think it's: >> >> * The kernel should use HMT_MEDIUM_LOW as it's "default" priority >> * The kernel should use HMT_LOW as it's "low" priority >> >>Which would imply: >> >> * The kernel should not use HMT_MEDIUM anywhere .. >> * Nor should it use any of the other higher HMT modes. >> >>Do you agree? Not entirely. HT_MEDIUM might still be used by the kernel, in places where a priority higher than the default is required. >>The reason I ask is I still see HMT_MEDIUM used in a few places, and it's not >>clear to me if that is correct. > > > HMT_MEDIUM used to be our default no ? Yes, but I am not sure that all references to HMT_MEDIUM were references to the default kernel priority. > Also there's an open question... when doing things with interrupts off > (or worse, in real mode) such as some KVM hcalls etc... should we on the > contrary boost up to limit interrupt latency ? Yes. I think that there are cases when one should consider using HT_MEDIUM. Shouldn't we define a new macro HMT_DEFAULT, to identify explicitely where the default priority is required? Philippe