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Thu, 15 Oct 2026 05:09:34 -0400 (EDT) X-Mailer: MessagingEngine.com Webmail Interface Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-ThreadId: AQvcS6cpqXYc Date: Thu, 15 Oct 2026 11:09:13 +0200 From: "Arnd Bergmann" To: "Ramin Moussavi" , "Andreas Larsson" , "David S . Miller" Cc: "Thomas Gleixner" , "Peter Zijlstra" , "Guenter Roeck" , sparclinux@vger.kernel.org, linux-kernel@vger.kernel.org Message-Id: <26e4d054-c1d6-4422-962c-e123269d36a9@app.fastmail.com> In-Reply-To: <20261015085545.3246951-3-ramin.moussavi@yacoub.de> References: <20261015085545.3246951-1-ramin.moussavi@yacoub.de> <20261015085545.3246951-3-ramin.moussavi@yacoub.de> Subject: Re: [PATCH 2/4] sparc32: wait for secondary CPUs by time, not by loop count Content-Type: text/plain Content-Transfer-Encoding: 7bit On Thu, Oct 15, 2026, at 10:55, Ramin Moussavi wrote: > smp4m_boot_one_cpu(), smp4d_boot_one_cpu() and leon_boot_one_cpu() give > a starting CPU 10000 rounds of udelay(200) to show up in cpu_callin_map, > which is meant to be two seconds. But udelay() is only as long as > loops_per_jiffy says. Under qemu the delay loop calibration varies from > boot to boot depending on host load -- on an emulated SPARCstation 20 > between 4 and 671 BogoMIPS for the same kernel and command line -- and > with a low value the wait shrinks to a few milliseconds. The boot CPU > then reports > The patch is not wrong, but having a broken udelay() is still problematic in other places, so it may be better to fix that instead. On most modern targets, we tend to just use the cycle counter if the frequency is known and avoid the delay loop calibration entirely. Any reason that sparc32 still needs the calibration? Arnd