From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail.linuxfoundation.org ([140.211.169.12]:57710 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S965236AbeALXdF (ORCPT ); Fri, 12 Jan 2018 18:33:05 -0500 Date: Fri, 12 Jan 2018 15:33:04 -0800 From: Andrew Morton To: Andrei Vagin Cc: linux-fsdevel@vger.kernel.org, Alexey Dobriyan , KAMEZAWA Hiroyuki Subject: Re: [PATCH 1/2] procfs: add seq_put_hex_ll to speed up /proc/pid/maps Message-Id: <20180112153304.f4a7dfbae2942e3fdd93eab9@linux-foundation.org> In-Reply-To: <20180112185812.7710-1-avagin@openvz.org> References: <20180112185812.7710-1-avagin@openvz.org> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-fsdevel-owner@vger.kernel.org List-ID: On Fri, 12 Jan 2018 10:58:11 -0800 Andrei Vagin wrote: > seq_put_hex_ll() prints a number in hexadecimal notation and works > faster than seq_printf(). > > ... > > --- a/fs/seq_file.c > +++ b/fs/seq_file.c > @@ -670,6 +670,26 @@ void seq_puts(struct seq_file *m, const char *s) > } > EXPORT_SYMBOL(seq_puts); > > +static inline void seq_put_delimeter(struct seq_file *m, const char *delimiter) > +{ > + int len; > + > + if (!delimiter || !delimiter[0]) > + return; > + > + if (delimiter[1] == 0) > + return seq_putc(m, delimiter[0]); > + > + len = strlen(delimiter); > + if (m->count + len >= m->size) { > + seq_set_overflow(m); > + return; > + } > + > + memcpy(m->buf + m->count, delimiter, len); > + m->count += len; > +} Can we please have a nice comment describing this function's role and behaviour? I don't think the `inline' is needed or desirable - gcc can figure that out, and with three callsites a `noinline' would be more justified! That `return seq_putc(...)' will generate a warning in some situations - seq_putc() returns void. Let's split it into 'seq_putc(...); return;' please. > +/** > + * seq_put_hex_ll - put a number in hexadecimal notation > + * @m: seq_file identifying the buffer to which data should be written > + * @delimiter: a string which is printed before the number > + * @v: the number > + * @width: a minimum field width > + * > + * seq_put_hex_ll(m, "", v, 8) is equal to seq_printf(m, "0x08llx", v) > + * > + * This routine is very quick when you show lots of numbers. > + * In usual cases, it will be better to use seq_printf(). It's easier to read. > + */ > +void seq_put_hex_ll(struct seq_file *m, const char *delimiter, > + unsigned long long v, int width) > +{ > + int i, len; > + > + seq_put_delimeter(m, delimiter); > + > + len = (sizeof(v) * 8 - __builtin_clzll(v) + 3) / 4; > + > + if (unlikely(len == 0)) > + len = 1; > + > + if (len < width) > + len = width; > + > + if (m->count + len > m->size) > + goto overflow; > + > + for (i = len - 1; i >= 0; i--) { > + m->buf[m->count + i] = hex_asc[0xf & v]; > + v = v >> 4; > + } > + m->count += len; > + return; > +overflow: > + seq_set_overflow(m); > +} I don't think we need the goto. Just do "seq_set_overflow(m); return;".