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Thu, 14 Mar 2024 09:35:04 -0700 (PDT) Message-ID: <06cedbcc-fee9-4a58-a0bb-42f6b594ccf8@suse.com> Date: Thu, 14 Mar 2024 17:35:02 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 2/7] xen/bitops: Implement ffs() in common logic Content-Language: en-US To: Andrew Cooper Cc: =?UTF-8?Q?Roger_Pau_Monn=C3=A9?= , Wei Liu , Stefano Stabellini , Julien Grall , Volodymyr Babchuk , Bertrand Marquis , Michal Orzel , Oleksii Kurochko , Shawn Anastasio , "consulting @ bugseng . com" , Simone Ballarin , Federico Serafini , Nicola Vetrini , Xen-devel References: <20240313172716.2325427-1-andrew.cooper3@citrix.com> <20240313172716.2325427-3-andrew.cooper3@citrix.com> <76a1e81d-86d1-438c-975e-c4db46af93ee@suse.com> <6a3c09a1-f35f-4d1e-bbba-342388da71ef@citrix.com> 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: <6a3c09a1-f35f-4d1e-bbba-342388da71ef@citrix.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit On 14.03.2024 17:23, Andrew Cooper wrote: > On 14/03/2024 2:16 pm, Jan Beulich wrote: >> On 13.03.2024 18:27, Andrew Cooper wrote: >>> --- a/xen/arch/arm/include/asm/bitops.h >>> +++ b/xen/arch/arm/include/asm/bitops.h >>> @@ -157,7 +157,7 @@ static inline int fls(unsigned int x) >>> } >>> >>> >>> -#define ffs(x) ({ unsigned int __t = (x); fls(ISOLATE_LSB(__t)); }) >>> +#define arch_ffs(x) ({ unsigned int __t = (x); fls(ISOLATE_LSB(__t)); }) >> The way the macro is invoked, I don't think the helper local variable >> is then needed anymore? > > I strongly suspect It is still needed.  ISOLATE_LSB() double-expands its > parameter. Even that double evaluation doesn't matter when the invoking entity is an inline function, and it doesn't use any non-trivial expression as argument. >>> --- a/xen/include/xen/bitops.h >>> +++ b/xen/include/xen/bitops.h >>> @@ -110,6 +110,21 @@ static inline int generic_flsl(unsigned long x) >>> >>> #include >>> >>> +/* >>> + * Find First Set bit. Bits are labelled from 1. >>> + */ >>> +static always_inline __pure unsigned int ffs(unsigned int x) >> Why always_inline? > > For all the normal reasons to counter Clang and GCC doing stupid things > with inlines that contain assembly. Hmm, there are issues when the asm() would look "complex" to the compiler, but that's not the case here. I was asking because, as you imply by how you responded, we may need to gain many more always_inline when at some time even you were arguing against overriding compiler decisions like this (unless I'm mis-remembering). Jan