linux-kernel - Re: [PATCH V5 4/7] jump_label: Sort entries of the same key by the code

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Message-ID: <b6e3350b-8d27-bac6-f3b3-2d98638bada1@redhat.com>
Date:   Mon, 15 Apr 2019 13:33:49 +0200
From:   Daniel Bristot de Oliveira <bristot@...hat.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     linux-kernel@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        "Steven Rostedt (VMware)" <rostedt@...dmis.org>,
        Jiri Kosina <jkosina@...e.cz>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Chris von Recklinghausen <crecklin@...hat.com>,
        Jason Baron <jbaron@...mai.com>, Scott Wood <swood@...hat.com>,
        Marcelo Tosatti <mtosatti@...hat.com>,
        Clark Williams <williams@...hat.com>, x86@...nel.org
Subject: Re: [PATCH V5 4/7] jump_label: Sort entries of the same key by the
 code

On 4/15/19 12:55 PM, Peter Zijlstra wrote:
> On Mon, Apr 01, 2019 at 10:58:16AM +0200, Daniel Bristot de Oliveira wrote:
>> In the batching mode, entries with the same key should also be sorted by the
>> code, enabling a bsearch() of a code/addr when updating a key.
> 
> Might be good to explain *why*.
> 
> We can see what the code does, explaining why we do things is what we
> have Changelogs for.

Ack! I will explain why,

>> Signed-off-by: Daniel Bristot de Oliveira <bristot@...hat.com>
>> Cc: Thomas Gleixner <tglx@...utronix.de>
>> Cc: Ingo Molnar <mingo@...hat.com>
>> Cc: Borislav Petkov <bp@...en8.de>
>> Cc: "H. Peter Anvin" <hpa@...or.com>
>> Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
>> Cc: Masami Hiramatsu <mhiramat@...nel.org>
>> Cc: "Steven Rostedt (VMware)" <rostedt@...dmis.org>
>> Cc: Jiri Kosina <jkosina@...e.cz>
>> Cc: Josh Poimboeuf <jpoimboe@...hat.com>
>> Cc: "Peter Zijlstra (Intel)" <peterz@...radead.org>
>> Cc: Chris von Recklinghausen <crecklin@...hat.com>
>> Cc: Jason Baron <jbaron@...mai.com>
>> Cc: Scott Wood <swood@...hat.com>
>> Cc: Marcelo Tosatti <mtosatti@...hat.com>
>> Cc: Clark Williams <williams@...hat.com>
>> Cc: x86@...nel.org
>> Cc: linux-kernel@...r.kernel.org
>> ---
>>  kernel/jump_label.c | 16 ++++++++++++++++
>>  1 file changed, 16 insertions(+)
>>
>> diff --git a/kernel/jump_label.c b/kernel/jump_label.c
>> index e666a4d6642a..8b7bfbba4cef 100644
>> --- a/kernel/jump_label.c
>> +++ b/kernel/jump_label.c
>> @@ -36,12 +36,28 @@ static int jump_label_cmp(const void *a, const void *b)
>>  	const struct jump_entry *jea = a;
>>  	const struct jump_entry *jeb = b;
>>  
>> +	/*
>> +	 * Entrires are sorted by key.
>> +	 */

and this the typo above (just noticed),

>>  	if (jump_entry_key(jea) < jump_entry_key(jeb))
>>  		return -1;
>>  
>>  	if (jump_entry_key(jea) > jump_entry_key(jeb))
>>  		return 1;
>>  
>> +#ifdef HAVE_JUMP_LABEL_BATCH
>> +	/*
>> +	 * In the batching mode, entries should also be sorted by the code
>> +	 * inside the already sorted list of entries, enabling a bsearch in
>> +	 * the vector.
>> +	 */
>> +	if (jump_entry_code(jea) < jump_entry_code(jeb))
>> +		return -1;
>> +
>> +	if (jump_entry_code(jea) > jump_entry_code(jeb))
>> +		return 1;
>> +#endif
>> +
>>  	return 0;
>>  }
> 
> The secondary sort order doesn't hurt, so we could leave the #ifdef out,
> not sure.

and remove the #ifdef, unless someone else things we need to keep it.

-- Daniel