linux-kernel - Re: [PATCH] x86/fred: Optimize the FRED entry by prioritizing high-probability event dispatching

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Message-ID: <d96d60b9-fa17-4981-a7e9-1b8bab1a7eed@zytor.com>
Date: Thu, 16 Jan 2025 21:54:35 -0800
From: Xin Li <xin@...or.com>
To: Ethan Zhao <haifeng.zhao@...ux.intel.com>,
        "H. Peter Anvin"
 <hpa@...or.com>, Ethan Zhao <etzhao@...look.com>,
        linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc: tglx@...utronix.de, dave.hansen@...ux.intel.com, x86@...nel.org,
        andrew.cooper3@...rix.com, mingo@...hat.com, bp@...en8.de
Subject: Re: [PATCH] x86/fred: Optimize the FRED entry by prioritizing
 high-probability event dispatching

On 1/16/2025 9:18 PM, Ethan Zhao wrote:
>>
>> Just swap the 2 arguments, and it should be:
>> +    switch_likely (etype, EVENT_TYPE_OTHER) {
>>
>>
> after swapped the parameters as following:
> +#define switch_likely(v,l) \
> + switch((__typeof__(v))__builtin_expect((v),(l)))
> +
>   __visible noinstr void fred_entry_from_user(struct pt_regs *regs)
>   {
>          unsigned long error_code = regs->orig_ax;
> +       unsigned short etype = regs->fred_ss.type & 0xf;
> 
>          /* Invalidate orig_ax so that syscall_get_nr() works correctly */
>          regs->orig_ax = -1;
> 
> -       switch (regs->fred_ss.type) {
> +       switch_likely (etype, (EVENT_TYPE_EXTINT == etype || 
> EVENT_TYPE_OTHER == etype)) {

This is not what I suggested, the (l) argument should be only one
constant; __builtin_expect() doesn't allow 2 different constants.