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Wed, 22 Oct 2025 17:42:35 +0000 (GMT) Message-ID: Date: Wed, 22 Oct 2025 23:12:34 +0530 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [RESEND PATCH] sched/fair: Skip sched_balance_running cmpxchg when balance is not due From: Shrikanth Hegde To: Peter Zijlstra , Tim Chen Cc: Ingo Molnar , Chen Yu , Doug Nelson , Mohini Narkhede , linux-kernel@vger.kernel.org, Vincent Guittot , K Prateek Nayak References: <20251013142638.GM3245006@noisy.programming.kicks-ass.net> <20251014092436.GK4067720@noisy.programming.kicks-ass.net> <20251014094259.GR3245006@noisy.programming.kicks-ass.net> Content-Language: en-US In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-TM-AS-GCONF: 00 X-Authority-Analysis: v=2.4 cv=EJELElZC c=1 sm=1 tr=0 ts=68f91791 cx=c_pps a=GFwsV6G8L6GxiO2Y/PsHdQ==:117 a=GFwsV6G8L6GxiO2Y/PsHdQ==:17 a=IkcTkHD0fZMA:10 a=x6icFKpwvdMA:10 a=VkNPw1HP01LnGYTKEx00:22 a=VwQbUJbxAAAA:8 a=VnNF1IyMAAAA:8 a=CviSjgRic15PywDmuwwA:9 a=3ZKOabzyN94A:10 a=QEXdDO2ut3YA:10 a=cPQSjfK2_nFv0Q5t_7PE:22 X-Proofpoint-Spam-Details-Enc: AW1haW4tMjUxMDE4MDAyMiBTYWx0ZWRfXzJirS98xQmwK f8of/ry+Cc/eOLTE/wOHkNPFRc/E/gFHcinjqkc+vTE1t62K7c9sd4PjO/HBBpPOppG7YSp8RqA y6SifiWVfIxpNKZyzYONSm1oE9s7L6y07YUCbbDv4os82Ph4bIkGyCfSo7w50SyJFOc7DbzfngF PbWcGNwO4KY3AyHE5Sdsar5VQOpkhDVkXFovzLcXa5BddfVlsLCbGhFBYvbY58WTYKwnvSxaKbz kY6pkpVsMQKMmzzaa50gDRnjYdZn6tevIeP9Oq2k7cGsdWniGBRB/o8w6GnXRs9Ul/Jtzn3H28v auIThNJJKZKYYQvYOq9cMYadGq5iuFReRkhoIu5mph5g2x708PVDgQvak8ZOmLCzfIrWQ82rfjY 6H6pHgvOGhmaf17uOj1CLrwOmHcPIg== X-Proofpoint-GUID: TH4CJPMjnc-U-b4n-iX8YnAfxxSrAxzF X-Proofpoint-ORIG-GUID: TH4CJPMjnc-U-b4n-iX8YnAfxxSrAxzF X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1121,Hydra:6.1.9,FMLib:17.12.80.40 definitions=2025-10-22_07,2025-10-22_01,2025-03-28_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 impostorscore=0 priorityscore=1501 suspectscore=0 bulkscore=0 spamscore=0 malwarescore=0 phishscore=0 adultscore=0 lowpriorityscore=0 clxscore=1015 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.19.0-2510020000 definitions=main-2510180022 On 10/16/25 7:33 PM, Shrikanth Hegde wrote: > > > On 10/14/25 3:12 PM, Peter Zijlstra wrote: >> On Tue, Oct 14, 2025 at 03:03:41PM +0530, Shrikanth Hegde wrote: >> >>>> @@ -11758,6 +11775,12 @@ static int sched_balance_rq(int this_cpu, >>>> struct rq *this_rq, >>>>            goto out_balanced; >>>>        } >>>> +    if (idle != CPU_NEWLY_IDLE && (sd->flags & SD_SERIALIZE)) { >>>> +        if (atomic_cmpxchg_acquire(&sched_balance_running, 0, 1)) >>>> +            goto out_balanced; >>> >>> Maybe goto out instead of out_balanced ? >> >> That would be inconsistent with the !should_we_balance() goto >> out_balanced right above this, no? >> > Hi Peter. > > Did similar probe points numbers compared to this. Even the patch is > quite similar to what > was suggested there a while ago. > https://lore.kernel.org/all/41e11090-a100-48a7-a0dd- > c989772822d7@linux.ibm.com/ > > 480 CPUs system with 6 NUMA nodes. (different system than last time) > Hi Peter, Tim. How are we proceeding here? Should i send the below patch with changelog or is it being worked out by either of you. It is really beneficial for large systems to avoid un-neccessary cache bouncing. > tl;dr > > - Number of time sched_balance_running is taken is way less after the > swb check. (which is great) > - Number of time it fails to set is very low after swb. (So out_balanced > vs out may not make a > significant difference.) > - Patch is at the end. It is this patch + redo stuff + > (ref_variable_stuff(ignore)) > >