From: "H. Peter Anvin" <hpa@zytor.com>
To: David Laight <David.Laight@ACULAB.COM>,
"'Thorsten Blum'" <thorsten.blum@toblux.com>,
Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
Dave Hansen <dave.hansen@linux.intel.com>,
"x86@kernel.org" <x86@kernel.org>
Cc: "Peter Zijlstra (Intel)" <peterz@infradead.org>,
Wei Liu <wei.liu@kernel.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: RE: [PATCH] x86/apic: Use div64_ul() instead of do_div()
Date: Thu, 29 Feb 2024 17:01:43 -0800 [thread overview]
Message-ID: <96394DFF-43D7-4877-AA47-FC847FD26184@zytor.com> (raw)
In-Reply-To: <7e46123775e64898bd7c467328125ee0@AcuMS.aculab.com>
>>
>> Change deltapm to unsigned long and replace do_div() with div64_ul()
>> which doesn't implicitly cast the divisor and doesn't unnecessarily
>> calculate the remainder.
>
>Eh? they are entirely different beasts.
>
>do_div() does a 64 by 32 divide that gives a 32bit quotient.
>div64_ul() does a much more expensive 64 by 64 divide that
>can generate a 64bit quotient.
>
>The remainder is pretty much free in both cases.
>If a cpu has a divide instruction it will almost certainly
>put the result in one register and the quotient in another.
>
Not on e.g. RISC-V.
next prev parent reply other threads:[~2024-03-01 1:03 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-02-27 11:43 Thorsten Blum
2024-02-29 22:13 ` David Laight
2024-03-01 1:01 ` H. Peter Anvin [this message]
2024-03-01 8:53 ` David Laight
2024-03-01 12:28 ` Thorsten Blum
2024-03-01 20:39 ` [PATCH v2] x86/apic: Use u32 instead of unsigned long Thorsten Blum
2024-03-08 12:43 ` [RESEND PATCH " Thorsten Blum
2024-03-08 16:12 ` Dave Hansen
2024-03-08 19:50 ` Thorsten Blum
2024-03-08 23:02 ` [PATCH v3] x86/apic: Improve data types to fix Coccinelle warnings Thorsten Blum
2024-03-18 10:47 ` [RESEND PATCH " Thorsten Blum
2024-03-18 16:13 ` Dave Hansen
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