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([2603:8080:7400:36da:dff5:4180:2562:4c1e]) by smtp.gmail.com with ESMTPSA id 006d021491bc7-601db67bc6csm1998224eaf.12.2025.03.18.05.09.42 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 18 Mar 2025 05:09:42 -0700 (PDT) Message-ID: Date: Tue, 18 Mar 2025 07:09:41 -0500 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: [RFC] panic: reduce CPU consumption when finished handling panic From: Carlos Bilbao To: pmladek@suse.com, Andrew Morton , jani.nikula@intel.com, open list , Greg Kroah-Hartman , Thomas Gleixner , takakura@valinux.co.jp, john.ogness@linutronix.de References: Content-Language: en-US Cc: jglauber@digitalocean.com In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit +CCed Jan Glauber as he'd figure as Co-developed-by if this goes through. Thanks, Carlos On 3/17/25 17:01, Carlos Bilbao wrote: > After the kernel has finished handling a panic, it enters a busy-wait loop. > But, this unnecessarily consumes CPU power and electricity. Plus, in VMs, > this negatively impacts the throughput of other VM guests running on the > same hypervisor. > > I propose introducing a function cpu_halt_end_panic() to halt the CPU > during this state while still allowing interrupts to be processed. See my > commit below. > > Thanks in advance! > > Signed-off-by: Carlos Bilbao > --- >  kernel/panic.c | 17 ++++++++++++++++- >  1 file changed, 16 insertions(+), 1 deletion(-) > > diff --git a/kernel/panic.c b/kernel/panic.c > index fbc59b3b64d0..c00ccaa698d5 100644 > --- a/kernel/panic.c > +++ b/kernel/panic.c > @@ -276,6 +276,21 @@ static void panic_other_cpus_shutdown(bool crash_kexec) >          crash_smp_send_stop(); >  } >   > +static void cpu_halt_end_panic(void) > +{ > +#ifdef CONFIG_X86 > +    native_safe_halt(); > +#elif defined(CONFIG_ARM) > +    cpu_do_idle(); > +#else > +    /* > +     * Default to a simple busy-wait if no architecture-specific halt is > +     * defined above > +     */ > +    mdelay(PANIC_TIMER_STEP); > +#endif > +} > + >  /** >   *    panic - halt the system >   *    @fmt: The text string to print > @@ -474,7 +489,7 @@ void panic(const char *fmt, ...) >              i += panic_blink(state ^= 1); >              i_next = i + 3600 / PANIC_BLINK_SPD; >          } > -        mdelay(PANIC_TIMER_STEP); > +        cpu_halt_end_panic(); >      } >  } >