1404788 - Poor FileReader performance when reading large files in Windows FF 55.01b1 - 56.0

Status: RESOLVED DUPLICATE of bug 1397645

(Core :: DOM: Core & HTML, defect, P2)

Description

[karthik.l.kailash]

User Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/61.0.3163.100 Safari/537.36

Steps to reproduce:

When using `FileReader` or `FileReaderSync` in Firefox on Windows, the latency of calls to `readAsArrayBuffer()` linearly increases as I progress through more of the file.

I created some tests to demonstrate this.  For each of the links below, once you select a file it will print how many milliseconds each 1MB read took.  After reading the entire file, it prints an array containing all the read times.

 - FileReaderSync in web worker:  https://jsfiddle.net/eawpdabh/5/
 - FileReader in web worker: https://jsfiddle.net/jbn3ra87/9/
 - FileReader not in worker:  https://jsfiddle.net/rnt6zpr2/4/



Actual results:

Testing done on desktop running Windows 10 with 4.4GHz i7-6700K and 16GB DDR4 RAM, SSD.  Using a 1GB file and the JSFiddles posted above, which read 1MB at a time sequentially.

On Firefox versions 55.0b1 through 56.0, the latency of calls to readAsArrayBuffer() linearly increases with subsequent calls.  On a 1GB file, the first call to read 1MB takes around 1ms, the 1024th takes over 400ms!


Expected results:

read() times should stay constant (around 1ms for 1MB read on my machine).  It looks like the problem no longer exists in the 57.0b4 release, would it be possible to backport a fix for 56.0 as well?

Full results of my testing are available in this Box Note: 
 https://cloud.box.com/s/wbpkld4ethn0avglnmng51uc7iuo5kqe

Comment 1

[karthik.l.kailash]

I can reproduce this problem on Windows 7 and 8 as well.

Comment 2

[Andrew Overholt [:overholt]]

I feel like we've had a similar report. baku, do you remember?

Comment 3

[Andrea Marchesini [:baku]]

This bug has been fixed by bug 1397645.