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charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-TM-AS-GCONF: 00 X-Proofpoint-GUID: _joylYGygdtjOVvlXLWsyk_kZsXz7h1w X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYwMTI3MDA4OCBTYWx0ZWRfXyJn1tAmmZz4h lTE/qM6H8to2jRXHKgcwXH827SsBl0nQSngGsYiNMzqwCfZZvyPNKquN2UciURehupBJHDExQaZ RmExRfwXGu5c3dZ1KEnmd/ueiwOLcoRo1EDyeDMCVneMBONrsaDSjgaG+9jjhJXsfh98gsFjhG8 pOrelhbs2N1+a2HBEAROuFpWTI0WtWm9BLYE+2OKzFtAz2leV5jtA6CRUXh/GNOClnJQvK1IU2O ZlgTWk06D7ZiVAJE6BGWDGOF4qNrQiI7yakE0qpSih7JoTpaUPad93TkMjBMdffwTjklGpfYrhC ce8eMbvMhXckxNL1FXmMLkklikrxVSN4CO24J/sB2G7WtjI1//fS4Wgj5e97YIvgaOfafphrobx T2O/zAESQxJO2mbYW+XZAFb2Q671mHfwllJO/GlOpYafFXdakQv3eNo/qNEall1VCNWDYwKkSzf +J2dGpeEZ+CBbUL35Hg== X-Authority-Analysis: v=2.4 cv=Zs3g6t7G c=1 sm=1 tr=0 ts=69789bcf cx=c_pps a=aDMHemPKRhS1OARIsFnwRA==:117 a=aDMHemPKRhS1OARIsFnwRA==:17 a=IkcTkHD0fZMA:10 a=vUbySO9Y5rIA:10 a=VkNPw1HP01LnGYTKEx00:22 a=VxO8rJwniCip0SPHUPYA:9 a=QEXdDO2ut3YA:10 X-Proofpoint-ORIG-GUID: cq9UUQAhTDXZ213DWwiSQg4oNb3OClnj X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1121,Hydra:6.1.20,FMLib:17.12.100.49 definitions=2026-01-27_02,2026-01-26_01,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 clxscore=1015 lowpriorityscore=0 adultscore=0 phishscore=0 suspectscore=0 bulkscore=0 impostorscore=0 priorityscore=1501 malwarescore=0 spamscore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.19.0-2601150000 definitions=main-2601270088 Hi Wangyang, Prateek. On 1/27/26 12:55 PM, Wangyang Guo wrote: > Read-mostly sched_clock_irqtime may share the same cacheline with > frequently updated nohz struct. Make it as static_key to avoid > false sharing issue. > > The only user of disable_sched_clock_irqtime() > is tsc_.*mark_unstable() which may be invoked under atomic context > and require a workqueue to disable static_key. But both of them > calls clear_sched_clock_stable() just before doing > disable_sched_clock_irqtime(). We can reuse > "sched_clock_work" to also disable sched_clock_irqtime(). > > One additional case need to handle is if the tsc is marked unstable > before late_initcall() phase, sched_clock_work will not be invoked > and sched_clock_irqtime will stay enabled although clock is unstable: > tsc_init() > enable_sched_clock_irqtime() # irqtime accounting is enabled here > ... > if (unsynchronized_tsc()) # true > mark_tsc_unstable() > clear_sched_clock_stable() > __sched_clock_stable_early = 0; > ... > if (static_key_count(&sched_clock_running.key) == 2) > # Only happens at sched_clock_init_late() > __clear_sched_clock_stable(); # Never executed > ... > > # late_initcall() phase > sched_clock_init_late() > if (__sched_clock_stable_early) # Already false > __set_sched_clock_stable(); # sched_clock is never marked stable > # TSC unstable, but sched_clock_work won't run to disable irqtime > > So we need to disable_sched_clock_irqtime() in sched_clock_init_late() > if clock is unstable. > Do you this as a valid case? have you tested with CONFIG_PARAVIRT? Lets say you have a non native sched clock such as kvm_sched_clock_read. tsc_init -> sets enable_sched_clock_irqtime() ->mark_tsc_unstable -> if using_native_sched_clock -> clear_sched_clock_stable In this case, since clear_sched_clock_stable won't be called you may not disable the sched clock irqtime since __sched_clock_stable_early is reset only in clear_sched_clock_stable Bigger concern(maybe) is clock source marked as stable still, though called mark_tsc_unstable in non native sched clock? Disclaimer: (just curious, seeing this x86 code for first time, so may not know all paths)