From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753076AbdEFQwA (ORCPT ); Sat, 6 May 2017 12:52:00 -0400 Received: from mx0a-001b2d01.pphosted.com ([148.163.156.1]:52300 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750967AbdEFQvw (ORCPT ); Sat, 6 May 2017 12:51:52 -0400 Date: Sat, 6 May 2017 09:51:47 -0700 From: "Paul E. McKenney" To: Ingo Molnar Cc: linux-kernel@vger.kernel.org Subject: Re: FYI, tiny-kernel fix for rcu_segcblist separate .c file Reply-To: paulmck@linux.vnet.ibm.com References: <20170505161351.GH3956@linux.vnet.ibm.com> <20170506071551.owtodttlhwvjrtzp@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20170506071551.owtodttlhwvjrtzp@gmail.com> User-Agent: Mutt/1.5.21 (2010-09-15) X-TM-AS-GCONF: 00 x-cbid: 17050616-0008-0000-0000-000002132A2D X-IBM-SpamModules-Scores: X-IBM-SpamModules-Versions: BY=3.00007029; HX=3.00000240; KW=3.00000007; PH=3.00000004; SC=3.00000209; SDB=6.00856944; UDB=6.00424393; IPR=6.00636306; BA=6.00005328; NDR=6.00000001; ZLA=6.00000005; ZF=6.00000009; ZB=6.00000000; ZP=6.00000000; ZH=6.00000000; ZU=6.00000002; MB=3.00015339; XFM=3.00000014; UTC=2017-05-06 16:51:49 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 17050616-0009-0000-0000-0000352A6218 Message-Id: <20170506165147.GR3956@linux.vnet.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10432:,, definitions=2017-05-06_12:,, signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 spamscore=0 suspectscore=0 malwarescore=0 phishscore=0 adultscore=0 bulkscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1703280000 definitions=main-1705060153 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sat, May 06, 2017 at 09:15:51AM +0200, Ingo Molnar wrote: > > * Paul E. McKenney wrote: > > > Hello, Ingo, > > > > Just in case you get complaints about kernel size... > > > > In response to Linus's feedback, I did commit 98059b98619d ("rcu: > > Separately compile large rcu_segcblist functions"), which of course > > has the side-effect of bloating Tiny SRCU, which 0day Test Robot > > complains about. > > > > So I have queued commit 7bf7fa5acc92 ("srcu: Apply trivial callback > > lists to shrink Tiny SRCU"), which makes up for the bloating and then some. > > > > I don't believe that this debloating is at all urgent because people > > building kernels for small-memory devices have to do a lot of other > > tweaking, so that applying this additional commit as a patch should > > not be too much incremental pain. > > > > So again, if you get complaints about 98059b98619d bloating tiny > > kernel builds, 7bf7fa5acc92 is the fix. > > Ok! > > I do agree that it's not urgent: single CPU systems are rapidly becoming the > exception for new hardware designed, even for embedded systems. At this point > I think the educational value of TinyRCU is its main quality. To your point, Tiny SRCU certainly is now quite self-contained and easy to understand. It is arguably even simpler than Tiny RCU because there are explicit wakeups -- no indirect reasoning about context switches required. Some people tell me that IoT-style microcontrollers for small devices require things like Tiny {S,}RCU, with one prominent recent example being Nicolas Pitre with his Tiny TTY layer. On the other hand, perhaps your argument about educational value applies to the TTY layer as well as to RCU. Maybe even more so -- it is quite possible that there are more people who understand RCU than understand the TTY layer. ;-) Thanx, Paul