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Fri, 5 Sep 2025 07:43:42 +0000 (GMT) Precedence: bulk X-Mailing-List: kvm@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset=UTF-8 Date: Fri, 05 Sep 2025 09:43:37 +0200 Message-Id: From: "Christoph Schlameuss" Cc: "KVM" , "David Hildenbrand" , "Heiko Carstens" , "Vasily Gorbik" , "Alexander Gordeev" , "Sven Schnelle" , To: "Christian Borntraeger" , "Janosch Frank" , "Claudio Imbrenda" Subject: Re: [PATCH] KVM: s390: improve interrupt cpu for wakeup X-Mailer: aerc 0.20.1 References: <20250904113927.119306-1-borntraeger@linux.ibm.com> In-Reply-To: <20250904113927.119306-1-borntraeger@linux.ibm.com> X-TM-AS-GCONF: 00 X-Proofpoint-Spam-Details-Enc: AW1haW4tMjUwODMwMDAzMCBTYWx0ZWRfX14r5aih/Splu 72cMGFmY03GlsgO06eB44uaB+h4uCcHm77ygZdodtKwAl37sv75w9hDgMNVNIyrehJ22OvrIT0X w/fSI4uLCGzTatBVeS9pVLcW+8F9eXIPubbaknN03O/z4js9VnjI1UWwUMUXiaEnlvNXGeTf0EK M1lT+qs++5m/I/yXT+TALB9G+tGuhowSYjSwKXe0Alz9jHaI0nzF88VeMFZh6YXU53Ip17Pp5vf ZCTam5spswRIqH6/fEBXIVNIf+hmR/hKx7I49/6g3pT5tAJPPbZhEr5/vep/bObsEo1yYeqUncF pNm2oYTVqUJl9yhW/vbyaTCch46PglTKP4mGR887keAdv1BbZC/bTqKxBtxA04ukNxtZU8gIX+e 011tR7wH X-Proofpoint-GUID: QN5TsIlycp35FCTzzGvr0tUFfbUV62Dz X-Proofpoint-ORIG-GUID: QN5TsIlycp35FCTzzGvr0tUFfbUV62Dz X-Authority-Analysis: v=2.4 cv=Ao/u3P9P c=1 sm=1 tr=0 ts=68ba94b4 cx=c_pps a=aDMHemPKRhS1OARIsFnwRA==:117 a=aDMHemPKRhS1OARIsFnwRA==:17 a=IkcTkHD0fZMA:10 a=yJojWOMRYYMA:10 a=VnNF1IyMAAAA:8 a=nicAsf1XB8fbJ-_zqUgA:9 a=QEXdDO2ut3YA:10 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 clxscore=1015 phishscore=0 impostorscore=0 priorityscore=1501 spamscore=0 suspectscore=0 bulkscore=0 adultscore=0 malwarescore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.19.0-2507300000 definitions=main-2508300030 With nit fixed. Reviewed-by: Christoph Schlameu=C3=9F On Thu Sep 4, 2025 at 1:39 PM CEST, Christian Borntraeger wrote: > 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 ----------------------------------^ nit: vCPUs > 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 > --- > arch/s390/include/asm/kvm_host.h | 2 +- > arch/s390/kvm/interrupt.c | 20 +++++++++----------- > 2 files changed, 10 insertions(+), 12 deletions(-)