910795 - Investigate solutions to the slowdown caused by variadic string arguments

Status: RESOLVED FIXED

(Core :: DOM: Core & HTML, defect)

Description

[Julien Wajsberg [:julienw]]

From bug 814014 comment 41:

1)  Using a variadic means we have to copy the string, since the type is
nsTArray<nsString>.  This involves an allocation of the copied data and then
a deallocation.  In this testcase those make up, between the two of them,
42% of the post-change time (so about 180ns: 3x what the entire call used to
take).  For the specific case of variadic string arguments, we _could_ try
using an nsTArray<FakeDependentString> or some such.  It would be annoying,
but...  Alternately we could try something where we use nsTArray<nsString>
but rebind it as a dependent string.

Comment 1

[Boris Zbarsky [:bzbarsky]]

I have some patches that avoid the string copy and speed up the toggle() and add() testcases by about 2x as a result...

Comment 2

[Boris Zbarsky [:bzbarsky]]

Attachment: part 1. Add a way to Rebind() an nsString to be a dependent string.

Comment 3

[Boris Zbarsky [:bzbarsky]]

Attachment: part 2. Use the new Rebind() setup to avoid creating string copies for variadic string arguments.

Comment 4

[Olli Pettay [:smaug][[e-mail]]]

Comment on attachment 797437 [details] [diff] [review]
part 2.  Use the new Rebind() setup to avoid creating string copies for variadic string arguments.

uh, aTokens. How did that pass my eyes. Could you rename to tokens

Comment 5

[Boris Zbarsky [:bzbarsky]]

> Could you rename to tokens

Done.

Comment 6

[Boris Zbarsky [:bzbarsky]]

   https://hg.mozilla.org/integration/mozilla-inbound/rev/d42f8528d09f
   https://hg.mozilla.org/integration/mozilla-inbound/rev/3e07ffec398e

Comment 7

[Ed Morley [:emorley]]

https://hg.mozilla.org/mozilla-central/rev/d42f8528d09f
https://hg.mozilla.org/mozilla-central/rev/3e07ffec398e