From: "Herman, Géza" <geza.herman@gmail.com>
To: Robert Thorpe <rt@robertthorpeconsulting.com>
Cc: help-gnu-emacs@gnu.org
Subject: Re: Strange shell mode performance
Date: Wed, 21 Oct 2020 12:27:33 +0200 [thread overview]
Message-ID: <e1ed5c18-5274-c837-fceb-d01d22a97b3d@gmail.com> (raw)
In-Reply-To: <877drkmkqs.fsf@robertthorpeconsulting.com>
The bug is caused by process-adaptive-read-buffering.
I analyzed the issue. For my use case, I made shell ~60x faster by
simple modifications (details:
https://debbugs.gnu.org/cgi/bugreport.cgi?bug=44007).
On 2020-10-21 03:27, Robert Thorpe wrote:
> I suspect that this is about memory allocation.
>
> I've noticed strange things like this before with large shell buffers.
> I don't think that pressing enter is really what makes the difference.
>
> I expect it's the memory that Emacs has allocated. When you have a
> small shell buffer you're usually reusing memory that has already been
> allocated to Emacs. That's because Emacs is constantly allocating and
> deallocating memory within it's own memory management. AFAIK it never
> actually gives memory back to the OS (modern OSes don't really need that anyway).
>
> However, when the size of the shell buffer rises above the largest size
> that the Emacs process have ever been things change. Then new memory
> has to be allocated to Emacs.
>
> I may be wrong about this though, it was ages since I looked at the
> code.
>
> BR,
> Robert Thorpe
>
> Herman, Géza <geza.herman@gmail.com> writes:
>
>> Hi all,
>>
>> I'm experiencing strange shell (comint) mode performance. If I cat a 10
>> MB file, it takes 1:20 to cat it. Emacs uses only 30% cpu. But, if I
>> press enter after I send the cat command, it speeds up, and it only
>> takes 8 sec (emacs cpu usage goes up to 100%).
>>
>> Same thing: if I execute "seq 100000" in a small emacs window, it takes
>> ~3 seconds. But, if I press enter after executing seq, it takes only 0.4
>> sec (this is not 100% reproducible, sometimes pressing enter doesn't
>> make a difference).
>> (I executed comint-clear-buffer before measurements)
>>
>> It happens with 26.3 and ~3-week-old master branch as well, without any
>> extra config (emacs -Q).
>>
>> Any ideas what causes this? Would it be possible to always have the
>> better performance without needing to press enter?
>>
>> Thanks,
>> Geza
prev parent reply other threads:[~2020-10-21 10:27 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-10-14 10:49 Strange shell mode performance Herman, Géza
2020-10-14 17:32 ` Stefan Monnier
2020-10-21 1:27 ` Robert Thorpe
2020-10-21 10:27 ` Herman, Géza [this message]
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