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To: Sebastian Andrzej Siewior , linux-kernel@vger.kernel.org, linux-rt-devel@lists.linux.dev Cc: Ben Segall , Catalin Marinas , Dietmar Eggemann , Ingo Molnar , Juri Lelli , Mel Gorman , Peter Zijlstra , Steven Rostedt , Thomas Gleixner , Valentin Schneider , Vincent Guittot , Will Deacon References: <20250203141632.440554-1-bigeasy@linutronix.de> <20250203141632.440554-2-bigeasy@linutronix.de> From: Shrikanth Hegde Content-Language: en-US In-Reply-To: <20250203141632.440554-2-bigeasy@linutronix.de> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-TM-AS-GCONF: 00 X-Proofpoint-GUID: EPJptHoLEpY6kJzKaFTUubVcOttCPjEY X-Proofpoint-ORIG-GUID: tXWGLHMlr9CxQEQxlLh8GF5Fj2uROFWl X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1057,Hydra:6.0.680,FMLib:17.12.68.34 definitions=2025-02-08_03,2025-02-07_03,2024-11-22_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 adultscore=0 spamscore=0 priorityscore=1501 mlxscore=0 impostorscore=0 suspectscore=0 malwarescore=0 clxscore=1015 lowpriorityscore=0 mlxlogscore=999 bulkscore=0 phishscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.19.0-2501170000 definitions=main-2502080059 On 2/3/25 19:46, Sebastian Andrzej Siewior wrote: > The individual architectures often add the preemption model to the begin > of the backtrace. This is the case on X86 or ARM64 for the "die" case > but not for regular warning. With the addition of DYNAMIC_PREEMPT for > PREEMPT_RT we end up with CONFIG_PREEMPT and CONFIG_PREEMPT_RT set > simultaneously. That means that everyone who tried to add that piece of > information gets it wrong for PREEMPT_RT because PREEMPT is checked > first. > > Provide a generic function which returns the current scheduling model > considering LAZY preempt and the current state of PREEMPT_DYNAMIC. > [ The dynamic building of the string can lead to an empty string if the > function is invoked simultaneously on two CPUs. ] > > Co-developed-by: Peter Zijlstra (Intel) > Signed-off-by: Peter Zijlstra (Intel) > Co-developed-by: Steven Rostedt (Google) > Signed-off-by: Steven Rostedt (Google) > Signed-off-by: Sebastian Andrzej Siewior > --- > include/linux/preempt.h | 2 ++ > kernel/sched/core.c | 47 +++++++++++++++++++++++++++++++++++++++++ > kernel/sched/debug.c | 10 +++++---- > kernel/sched/sched.h | 1 + > 4 files changed, 56 insertions(+), 4 deletions(-) > > diff --git a/include/linux/preempt.h b/include/linux/preempt.h > index ca86235ac15c0..3e9808f2b5491 100644 > --- a/include/linux/preempt.h > +++ b/include/linux/preempt.h > @@ -515,6 +515,8 @@ static inline bool preempt_model_rt(void) > return IS_ENABLED(CONFIG_PREEMPT_RT); > } > > +extern const char *preempt_model_str(void); > + > /* > * Does the preemption model allow non-cooperative preemption? > * > diff --git a/kernel/sched/core.c b/kernel/sched/core.c > index 165c90ba64ea9..bd2664755b09a 100644 > --- a/kernel/sched/core.c > +++ b/kernel/sched/core.c > @@ -7646,10 +7646,57 @@ PREEMPT_MODEL_ACCESSOR(lazy); > > #else /* !CONFIG_PREEMPT_DYNAMIC: */ > > +#define preempt_dynamic_mode -1 > + > static inline void preempt_dynamic_init(void) { } > > #endif /* CONFIG_PREEMPT_DYNAMIC */ > > +const char *preempt_modes[] = { > + "none", "voluntary", "full", "lazy", NULL, > +}; > + > +const char *preempt_model_str(void) > +{ > + bool brace = IS_ENABLED(CONFIG_PREEMPT_RT) && > + (IS_ENABLED(CONFIG_PREEMPT_DYNAMIC) || > + IS_ENABLED(CONFIG_PREEMPT_LAZY)); > + static char buf[128]; > + > + if (IS_ENABLED(CONFIG_PREEMPT_BUILD)) { > + struct seq_buf s; > + > + seq_buf_init(&s, buf, 128); > + seq_buf_puts(&s, "PREEMPT"); > + > + if (IS_ENABLED(CONFIG_PREEMPT_RT)) > + seq_buf_printf(&s, "%sRT%s", > + brace ? "_{" : "_", > + brace ? "," : ""); > + > + if (IS_ENABLED(CONFIG_PREEMPT_DYNAMIC)) { > + seq_buf_printf(&s, "(%s)%s", > + preempt_dynamic_mode > 0 ? > + preempt_modes[preempt_dynamic_mode] : "undef", > + brace ? "}" : ""); > + return seq_buf_str(&s); > + } > + > + if (IS_ENABLED(CONFIG_PREEMPT_LAZY)) { > + seq_buf_printf(&s, "LAZY%s", > + brace ? "}" : ""); > + return seq_buf_str(&s); > + } > + > + return seq_buf_str(&s); > + } > + > + if (IS_ENABLED(CONFIG_PREEMPT_VOLUNTARY_BUILD)) > + return "VOLUNTARY"; > + > + return "NONE"; > +} nit: This means when it preempt=full, it is going to show PREEMPT or PREEMPT_RT. Maybe that could be put into changelog or add code similar to lazy for full as well, so it is easier for user to know if it is in preempt=full model. In all other models, there is a suffix like PREEMPTLAZY. Dynamic modes looks good. Reviewed-by: Shrikanth Hegde > + > int io_schedule_prepare(void) > { > int old_iowait = current->in_iowait; > diff --git a/kernel/sched/debug.c b/kernel/sched/debug.c > index fd7e852207157..755232ac88de9 100644 > --- a/kernel/sched/debug.c > +++ b/kernel/sched/debug.c > @@ -244,11 +244,13 @@ static ssize_t sched_dynamic_write(struct file *filp, const char __user *ubuf, > > static int sched_dynamic_show(struct seq_file *m, void *v) > { > - static const char * preempt_modes[] = { > - "none", "voluntary", "full", "lazy", > - }; > - int j = ARRAY_SIZE(preempt_modes) - !IS_ENABLED(CONFIG_ARCH_HAS_PREEMPT_LAZY); > int i = IS_ENABLED(CONFIG_PREEMPT_RT) * 2; > + int j; > + > + /* Count entries in NULL terminated preempt_modes */ > + for (j = 0; preempt_modes[j]; j++) > + ; > + j -= !IS_ENABLED(CONFIG_ARCH_HAS_PREEMPT_LAZY); > > for (; i < j; i++) { > if (preempt_dynamic_mode == i) > diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h > index 38e0e323dda26..fb4486ceb978a 100644 > --- a/kernel/sched/sched.h > +++ b/kernel/sched/sched.h > @@ -3619,6 +3619,7 @@ extern int preempt_dynamic_mode; > extern int sched_dynamic_mode(const char *str); > extern void sched_dynamic_update(int mode); > #endif > +extern const char *preempt_modes[]; > > #ifdef CONFIG_SCHED_MM_CID >