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Mon, 04 Aug 2025 00:10:32 -0700 (PDT) Message-ID: Date: Mon, 4 Aug 2025 09:10:34 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] console: make printk_ratelimit_{burst,ms} const To: dmkhn@proton.me Cc: "xen-devel@lists.xenproject.org" , Andrew Cooper , Julien Grall , Stefano Stabellini , Anthony PERARD , Michal Orzel , =?UTF-8?Q?Roger_Pau_Monn=C3=A9?= References: <5fcd1c68-6c18-4a1d-8a1d-f056bdb6cde9@suse.com> Content-Language: en-US From: Jan Beulich Autocrypt: addr=jbeulich@suse.com; keydata= xsDiBFk3nEQRBADAEaSw6zC/EJkiwGPXbWtPxl2xCdSoeepS07jW8UgcHNurfHvUzogEq5xk hu507c3BarVjyWCJOylMNR98Yd8VqD9UfmX0Hb8/BrA+Hl6/DB/eqGptrf4BSRwcZQM32aZK 7Pj2XbGWIUrZrd70x1eAP9QE3P79Y2oLrsCgbZJfEwCgvz9JjGmQqQkRiTVzlZVCJYcyGGsD /0tbFCzD2h20ahe8rC1gbb3K3qk+LpBtvjBu1RY9drYk0NymiGbJWZgab6t1jM7sk2vuf0Py O9Hf9XBmK0uE9IgMaiCpc32XV9oASz6UJebwkX+zF2jG5I1BfnO9g7KlotcA/v5ClMjgo6Gl MDY4HxoSRu3i1cqqSDtVlt+AOVBJBACrZcnHAUSuCXBPy0jOlBhxPqRWv6ND4c9PH1xjQ3NP nxJuMBS8rnNg22uyfAgmBKNLpLgAGVRMZGaGoJObGf72s6TeIqKJo/LtggAS9qAUiuKVnygo 3wjfkS9A3DRO+SpU7JqWdsveeIQyeyEJ/8PTowmSQLakF+3fote9ybzd880fSmFuIEJldWxp Y2ggPGpiZXVsaWNoQHN1c2UuY29tPsJgBBMRAgAgBQJZN5xEAhsDBgsJCAcDAgQVAggDBBYC AwECHgECF4AACgkQoDSui/t3IH4J+wCfQ5jHdEjCRHj23O/5ttg9r9OIruwAn3103WUITZee e7Sbg12UgcQ5lv7SzsFNBFk3nEQQCACCuTjCjFOUdi5Nm244F+78kLghRcin/awv+IrTcIWF hUpSs1Y91iQQ7KItirz5uwCPlwejSJDQJLIS+QtJHaXDXeV6NI0Uef1hP20+y8qydDiVkv6l IreXjTb7DvksRgJNvCkWtYnlS3mYvQ9NzS9PhyALWbXnH6sIJd2O9lKS1Mrfq+y0IXCP10eS FFGg+Av3IQeFatkJAyju0PPthyTqxSI4lZYuJVPknzgaeuJv/2NccrPvmeDg6Coe7ZIeQ8Yj t0ARxu2xytAkkLCel1Lz1WLmwLstV30g80nkgZf/wr+/BXJW/oIvRlonUkxv+IbBM3dX2OV8 AmRv1ySWPTP7AAMFB/9PQK/VtlNUJvg8GXj9ootzrteGfVZVVT4XBJkfwBcpC/XcPzldjv+3 HYudvpdNK3lLujXeA5fLOH+Z/G9WBc5pFVSMocI71I8bT8lIAzreg0WvkWg5V2WZsUMlnDL9 mpwIGFhlbM3gfDMs7MPMu8YQRFVdUvtSpaAs8OFfGQ0ia3LGZcjA6Ik2+xcqscEJzNH+qh8V m5jjp28yZgaqTaRbg3M/+MTbMpicpZuqF4rnB0AQD12/3BNWDR6bmh+EkYSMcEIpQmBM51qM EKYTQGybRCjpnKHGOxG0rfFY1085mBDZCH5Kx0cl0HVJuQKC+dV2ZY5AqjcKwAxpE75MLFkr wkkEGBECAAkFAlk3nEQCGwwACgkQoDSui/t3IH7nnwCfcJWUDUFKdCsBH/E5d+0ZnMQi+G0A nAuWpQkjM1ASeQwSHEeAWPgskBQL In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 01.08.2025 20:58, dmkhn@proton.me wrote: > On Fri, Aug 01, 2025 at 09:30:34AM +0200, Jan Beulich wrote: >> Them not being altered by any means, their __read_mostly attribute is >> actually counter-productive: It causes the compiler to instantiate the >> variables, when already with just the attributes dropped the compiler >> can constant-propagate the values into the sole use site. Make the >> situation yet more explicit by adding const. >> >> Also switch the variables away from being plain int, and have the >> parameters of __printk_ratelimit() follow suit. While there also >> similarly adjust the type of "missed" and "lost", and - while touching >> the adjacent line - increase lost_str[] to accommodate any unsigned >> 32-bit number. >> >> Fixes: a8b1845a7845 ("Miscellaneous data placement adjustments") >> Signed-off-by: Jan Beulich >> --- >> In principle {__,}printk_ratelimit() may also want to have their return >> type changed to bool, but I think doing so would go too far here: This >> would have knock-on effects elsewhere, and it would want considering to >> actually flip polarity. >> >> Despite the Fixes: tag I wouldn't consider this for backport. >> >> --- a/xen/drivers/char/console.c >> +++ b/xen/drivers/char/console.c >> @@ -1268,12 +1268,12 @@ void console_end_sync(void) >> * This enforces a rate limit: not more than one kernel message >> * every printk_ratelimit_ms (millisecs). >> */ >> -int __printk_ratelimit(int ratelimit_ms, int ratelimit_burst) >> +int __printk_ratelimit(unsigned int ratelimit_ms, unsigned int ratelimit_burst) >> { >> static DEFINE_SPINLOCK(ratelimit_lock); >> static unsigned long toks = 10 * 5 * 1000; >> static unsigned long last_msg; >> - static int missed; >> + static unsigned int missed; >> unsigned long flags; >> unsigned long long now = NOW(); /* ns */ >> unsigned long ms; >> @@ -1288,14 +1288,16 @@ int __printk_ratelimit(int ratelimit_ms, >> toks = ratelimit_burst * ratelimit_ms; >> if ( toks >= ratelimit_ms ) >> { >> - int lost = missed; >> + unsigned int lost = missed; >> + >> missed = 0; >> toks -= ratelimit_ms; >> spin_unlock(&ratelimit_lock); >> if ( lost ) >> { >> - char lost_str[8]; >> - snprintf(lost_str, sizeof(lost_str), "%d", lost); >> + char lost_str[10]; >> + >> + snprintf(lost_str, sizeof(lost_str), "%u", lost); > > Since this code is touched, I would also simplify the entire `if ( lost )` > block (I have it done in another experiment): > > char lost_str[64]; > size_t lost_len = snprintf(lost_str, sizeof(lost_str), > "printk: %d messages suppressed.\n", > lost_str); > > /* console_lock may already be acquired by printk(). */ > rspin_lock(&console_lock); > printk_start_of_line(CONSOLE_PREFIX, cflags); > __putstr(lost_str, lost_len); > ... > > What do you think? Maybe, but definitely not right in this patch. Jan