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Fri, 26 Apr 2024 07:46:24 GMT Received: from smtpav02.wdc07v.mail.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 2C10C58059; Fri, 26 Apr 2024 07:46:22 +0000 (GMT) Received: from smtpav02.wdc07v.mail.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id B21D258068; Fri, 26 Apr 2024 07:46:11 +0000 (GMT) Received: from [9.195.36.19] (unknown [9.195.36.19]) by smtpav02.wdc07v.mail.ibm.com (Postfix) with ESMTP; Fri, 26 Apr 2024 07:46:11 +0000 (GMT) Message-ID: <63314d92-9226-4005-a166-37c8648c5351@linux.ibm.com> Date: Fri, 26 Apr 2024 13:16:10 +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: [PATCH 00/30] PREEMPT_AUTO: support lazy rescheduling To: Linus Torvalds , Ankur Arora Cc: Thomas Gleixner , peterz@infradead.org, paulmck@kernel.org, akpm@linux-foundation.org, luto@kernel.org, bp@alien8.de, dave.hansen@linux.intel.com, hpa@zytor.com, mingo@redhat.com, juri.lelli@redhat.com, vincent.guittot@linaro.org, willy@infradead.org, mgorman@suse.de, jpoimboe@kernel.org, mark.rutland@arm.com, jgross@suse.com, andrew.cooper3@citrix.com, bristot@kernel.org, mathieu.desnoyers@efficios.com, geert@linux-m68k.org, glaubitz@physik.fu-berlin.de, anton.ivanov@cambridgegreys.com, mattst88@gmail.com, krypton@ulrich-teichert.org, rostedt@goodmis.org, David.Laight@aculab.com, richard@nod.at, mjguzik@gmail.com, jon.grimm@amd.com, bharata@amd.com, raghavendra.kt@amd.com, boris.ostrovsky@oracle.com, konrad.wilk@oracle.com, LKML , Michael Ellerman , Nicholas Piggin References: <20240213055554.1802415-1-ankur.a.arora@oracle.com> <74ffd154-5d92-4303-9977-6ddc9accdf01@linux.ibm.com> From: Shrikanth Hegde Content-Language: en-US In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-TM-AS-GCONF: 00 X-Proofpoint-GUID: nWFWbJqsO-Fjjm_oudoflrRyTLICP7cB X-Proofpoint-ORIG-GUID: Hx5mW6tmjG3ulb5NO5FRU3TgwmUOa5cD X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1011,Hydra:6.0.650,FMLib:17.11.176.26 definitions=2024-04-26_07,2024-04-26_01,2023-05-22_02 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 impostorscore=0 adultscore=0 priorityscore=1501 clxscore=1015 spamscore=0 phishscore=0 malwarescore=0 mlxlogscore=734 bulkscore=0 mlxscore=0 suspectscore=0 lowpriorityscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2404010000 definitions=main-2404260048 On 4/23/24 9:43 PM, Linus Torvalds wrote: > On Tue, 23 Apr 2024 at 08:23, Shrikanth Hegde wrote: >> >> >> Are these the only arch bits that need to be defined? am I missing something very >> basic here? will try to debug this further. Any inputs? > > I don't think powerpc uses the generic *_exit_to_user_mode() helper > functions, so you'll need to also add that logic to the low-level > powerpc code. > > IOW, on x86, with this patch series, patch 06/30 did this: > > - if (ti_work & _TIF_NEED_RESCHED) > + if (ti_work & (_TIF_NEED_RESCHED | _TIF_NEED_RESCHED_LAZY)) > schedule(); > > in kernel/entry/common.c exit_to_user_mode_loop(). > > But that works on x86 because it uses the irqentry_exit_to_user_mode(). > > On PowerPC, I think you need to at least fix up > > interrupt_exit_user_prepare_main() > > similarly (and any other paths like that - I used to know the powerpc > code, but that was long long LOOONG ago). > > Linus Thank you Linus for the pointers. That indeed did the trick. diff --git a/arch/powerpc/kernel/interrupt.c b/arch/powerpc/kernel/interrupt.c index eca293794a1e..f0f38bf5cea9 100644 --- a/arch/powerpc/kernel/interrupt.c +++ b/arch/powerpc/kernel/interrupt.c @@ -185,7 +185,7 @@ interrupt_exit_user_prepare_main(unsigned long ret, struct pt_regs *regs) ti_flags = read_thread_flags(); while (unlikely(ti_flags & (_TIF_USER_WORK_MASK & ~_TIF_RESTORE_TM))) { local_irq_enable(); - if (ti_flags & _TIF_NEED_RESCHED) { + if (ti_flags & (_TIF_NEED_RESCHED | _TIF_NEED_RESCHED_LAZY) ) { schedule(); } else { By adding LAZY checks in interrupt_exit_user_prepare_main, softlockup is no longer seen and hackbench results are more or less same on smaller system(96CPUS). However, I still see 20-50% regression on the larger system(320 CPUS). I will continue to debug why.