From: Alexey Dobriyan <adobriyan@gmail.com>
To: Andi Kleen <andi@firstfloor.org>
Cc: akpm@linux-foundation.org, linux-kernel@vger.kernel.org,
viro@zeniv.linux.org.uk
Subject: Re: [PATCH] proc: faster /proc/*/status
Date: Sun, 7 Aug 2016 11:53:22 +0300 [thread overview]
Message-ID: <20160807085322.GB1871@p183.telecom.by> (raw)
In-Reply-To: <87ziop46b8.fsf@tassilo.jf.intel.com>
On Sat, Aug 06, 2016 at 08:16:27PM -0700, Andi Kleen wrote:
> Alexey Dobriyan <adobriyan@gmail.com> writes:
> > -
> > + seq_printf(m, "State:\t%s", get_task_state(p));
> > +
> > + seq_puts(m, "\nTgid:\t");
>
> The only different should be the format string.
>
> Scanning the format string really shouldn't be that expensive?!?
Surprise, it is (see my reply to Al).
What seq_put_decimal_ull() did is the equivalent of
seq << "foo";
seq << bar;
seq << '\n';
No precisions, not widths, no padding, no upper and lowercasing.
> It would be better if you could find out why that is slow and optimize
> it. Then you would benefit every seq_printf user, not just this
> special case.
>
> Perhaps it could benefit from some of the bit masking tricks to
> scan the string with wider tests than a word.
And then what? Parsing format string is still be there.
This is first line of profile of the first function (format_decode)
│ static noinline_for_stack
│ int format_decode(const char *fmt, struct printf_spec *spec)
│ {
10.38 │ push %rbp <===
1.07 │ mov %rsp,%rbp
1.09 │ push %r12
4.51 │ mov %rsi,%r12
1.40 │ push %rbx
1.86 │ mov %rdi,%rbx
│ sub $0x8,%rsp
It is so bloated that gcc needs to be asked to not screw up with stack
size.
next prev parent reply other threads:[~2016-08-07 8:53 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-08-06 12:56 [PATCH] proc: faster /proc/*/status Alexey Dobriyan
2016-08-06 22:41 ` Joe Perches
2016-08-09 3:02 ` [PATCH] seq/proc: Modify seq_put_decimal_[u]ll to take a const char *, not char Joe Perches
2016-08-07 3:16 ` [PATCH] proc: faster /proc/*/status Andi Kleen
2016-08-07 8:53 ` Alexey Dobriyan [this message]
2016-08-07 16:59 ` Andi Kleen
2016-08-07 17:39 ` Joe Perches
2016-08-07 17:44 ` Andi Kleen
2016-08-07 21:22 ` Joe Perches
2016-08-09 23:25 ` Andrew Morton
2016-08-10 6:38 ` [RFC PATCH] meminfo: Break apart a very long seq_printf with #ifdefs Joe Perches
2016-08-11 21:50 ` Andrew Morton
2016-08-11 21:57 ` Joe Perches
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