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Tue, 25 Jun 2019 01:02:16 +0000 (GMT) Received: from Juliets-MacBook-Pro.local (unknown [9.80.219.73]) by b03ledav001.gho.boulder.ibm.com (Postfix) with ESMTPS; Tue, 25 Jun 2019 01:02:16 +0000 (GMT) Subject: Re: [PATCH] powerpc/rtas: retry when cpu offline races with suspend/migration To: Nathan Lynch , mmc References: <20190621060518.29616-1-nathanl@linux.ibm.com> <87h88eucbn.fsf@linux.ibm.com> From: Juliet Kim Message-ID: <5a825cec-234a-ee8a-a776-8ba305f9cb26@linux.vnet.ibm.com> Date: Mon, 24 Jun 2019 20:02:15 -0500 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.14; rv:60.0) Gecko/20100101 Thunderbird/60.7.2 MIME-Version: 1.0 In-Reply-To: <87h88eucbn.fsf@linux.ibm.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 8bit Content-Language: en-US X-TM-AS-GCONF: 00 X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:, , definitions=2019-06-25_01:, , signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 priorityscore=1501 malwarescore=0 suspectscore=0 phishscore=0 bulkscore=0 spamscore=0 clxscore=1011 lowpriorityscore=0 mlxscore=0 impostorscore=0 mlxlogscore=999 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1810050000 definitions=main-1906250004 X-BeenThere: linuxppc-dev@lists.ozlabs.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: ego@linux.vnet.ibm.com, linuxppc-dev@lists.ozlabs.org, julietk@linux.ibm.com Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Sender: "Linuxppc-dev" There's some concern this could retry forever, resulting in live lock.  Another approach would be to abandon the attempt and fail the LPM request. https://lists.ozlabs.org/pipermail/linuxppc-dev/2019-June/192531.html On 6/24/19 12:23 PM, Nathan Lynch wrote: > Hi Mingming, > > mmc writes: >> On 2019-06-21 00:05, Nathan Lynch wrote: >>> So return -EAGAIN instead of -EBUSY when this race is >>> encountered. Additionally: logging this event is still appropriate but >>> use pr_info instead of pr_err; and remove use of unlikely() while here >>> as this is not a hot path at all. >> Looks good, since it's not a hot path anyway, so unlikely() should >> benefit from optimize compiler path, and should stay. No? > The latency of this path in rtas_ibm_suspend_me() in the best case is > around 2-3 seconds. > > So I think not -- this is such a heavyweight and relatively > seldom-executed path that the unlikely() cannot yield any discernible > performance benefit, and its presence imposes a readability cost.