linux-kernel - Re: [PATCH] seq_file: Optimize seq

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Date: Fri, 19 Apr 2024 22:38:15 +0200
From: Christophe JAILLET <christophe.jaillet@...adoo.fr>
To: David Laight <David.Laight@...LAB.COM>,
 'Al Viro' <viro@...iv.linux.org.uk>
Cc: Christian Brauner <brauner@...nel.org>, Jan Kara <jack@...e.cz>,
 "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
 "kernel-janitors@...r.kernel.org" <kernel-janitors@...r.kernel.org>,
 "linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>
Subject: Re: [PATCH] seq_file: Optimize seq_puts()

Le 16/04/2024 à 22:56, David Laight a écrit :
> From: Al Viro
>> Sent: 15 April 2024 22:01
> ...
>> No need to make it a macro, actually.  And I would suggest going
>> a bit further:
>>
>> static inline void seq_puts(struct seq_file *m, const char *s)
> 
> That probably needs to be 'always_inline'.
> 
>> {
>> 	if (!__builtin_constant_p(*s))
>> 		__seq_puts(m, s);
>> 	else if (s[0] && !s[1])
>> 		seq_putc(m, s[0]);
>> 	else
>> 		seq_write(m, s, __builtin_strlen(s));
>> }
> 
> You missed seq_puts(m, "");
> 
> I did wonder about checking sizeof(s) <= 2 in the #define version.

git grep seq_puts.*\"[^\\].\" | wc -l
77

What would you do in this case?
2 seq_putc() in order to save a memcpy(..., 2), that's it?

It would also slightly change the behaviour, as only the 1st char could 
be added. Actually, it is all or nothing.

Don't know what is the best.

Any thought?

CJ


> That would pick up the cases where a separator is changed/added
> in a loop.
> 
> Could you do:
> 	size_t len = __builtin_strlen(s);
> 	if (!__builtin_constant_p(len))
> 		__seq_puts(m, s);
> 	else switch (len){
> 	case 0: break;
> 	case 1: seq_putc(m, s[0]);
> 	default: seq_write(m, s, len);
> 	}
> 
> 	David
> 
> -
> Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK
> Registration No: 1397386 (Wales)
> 
> 
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