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Fri, 5 Sep 2025 07:39:49 +0000 (GMT) Message-ID: <46a981a1-84fb-4f35-bb91-da4f0d6b1378@linux.ibm.com> Date: Fri, 5 Sep 2025 09:39:47 +0200 Precedence: bulk X-Mailing-List: linux-s390@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] KVM: s390: improve interrupt cpu for wakeup To: Janosch Frank , Claudio Imbrenda Cc: KVM , David Hildenbrand , Heiko Carstens , Vasily Gorbik , Alexander Gordeev , Sven Schnelle , linux-s390@vger.kernel.org References: <20250904113927.119306-1-borntraeger@linux.ibm.com> Content-Language: en-US From: Christian Borntraeger In-Reply-To: <20250904113927.119306-1-borntraeger@linux.ibm.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-TM-AS-GCONF: 00 X-Proofpoint-GUID: Iz40JNIrcRe2OQNjxPKvLl-wHC-OgXCo X-Authority-Analysis: v=2.4 cv=do3bC0g4 c=1 sm=1 tr=0 ts=68ba93cb cx=c_pps a=aDMHemPKRhS1OARIsFnwRA==:117 a=aDMHemPKRhS1OARIsFnwRA==:17 a=IkcTkHD0fZMA:10 a=yJojWOMRYYMA:10 a=VnNF1IyMAAAA:8 a=O1rW9cO9ph_K1hW2cTAA:9 a=QEXdDO2ut3YA:10 X-Proofpoint-ORIG-GUID: Iz40JNIrcRe2OQNjxPKvLl-wHC-OgXCo X-Proofpoint-Spam-Details-Enc: AW1haW4tMjUwOTAyMDA0MCBTYWx0ZWRfXwJQcM8sCCVZS XbvgsM3k7JKP/0x/ipvUzpR6rLM1a/skRk1wVM5Dcjk3Wpz9BBMeQ4DqonC2DIA3nz/o4IX0Yte AA1PbLTT6JUC0yLn6LlJ9SpCT+bchZ4708wkvWd3QXbML0NJbuRSdvxXmjEQ4FWFPQPCbkK89in 7QcJBXTqv7xZvgm3RxxuBlz+8oAdd4+LiXyqLPp1ab3/j6v0LN+Z7yr9SyLbdlAeHe7mVtFUPU6 x6L4nCnHxFVT7/g0/ltNnkZ3ZTudMhxrslzd9wJRlLjjyuIa1Wdixb74VJ6Djn6ZRbnRnIRcVHc yMjdtVmSvO9a3wNVj4Y5wvQKZP3agmot1HNuHdQMNsvwKYluxkgRW7fb4C5E/Lt8pV2N8sRAvHB vYQgXyWR X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1117,Hydra:6.1.9,FMLib:17.12.80.40 definitions=2025-09-05_02,2025-09-04_01,2025-03-28_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 phishscore=0 clxscore=1015 impostorscore=0 bulkscore=0 suspectscore=0 malwarescore=0 spamscore=0 priorityscore=1501 adultscore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.19.0-2507300000 definitions=main-2509020040 Am 04.09.25 um 13:39 schrieb Christian Borntraeger: > Turns out that picking an idle CPU for floating interrupts has some > negative side effects. The guest will keep the IO workload on its CPU > and rather use an IPI from the interrupt CPU instead of moving workload. > For example a guest with 2 vCPUss and 1 fio process might run that fio on > vcpu1. If after diag500 both vCPUs are idle then vcpu0 is woken up. The > guest will then do an IPI from vcpu0 to vcpu1. > > So lets change the heuristics and prefer the last CPU that went to > sleep. This one is likely still in halt polling and can be woken up > quickly. > > This patch shows significant improvements in terms of bandwidth or > cpu consumption for fio and uperf workloads and seems to be a net > win. > > Signed-off-by: Christian Borntraeger applied internally for CI regression runs. Will push to next if successful.