1954724 - Pathological SSLBuffer Performance

Status: RESOLVED FIXED

(NSS :: Libraries, enhancement, P1)

Description

[Dennis Jackson]

sslBuffers are widely used in libssl. These buffers are dynamically resizable with sslBuffer_Grow which can be invoked explicitly, or via calls to functions like sslBuffer_Append, sslBuffer_AppendNumber, sslBuffer_AppendVariable which always invoke sslBuffer_Grow. Unfortunately, every sslBuffer_Grow invocation grows the buffer by at least 1024 bytes via realloc, even if the buffer already had the requested space available.

In a benchmark of 1000 connections using an optimized build of tstclnt, we spend ~600ms inside realloc out of 14 CPU seconds total. Heaptrack shows ~102 reallocs per handshake from sslBuffer_Grow, which is roughly 20% of the total allocations made during a handshake.

Comment 1

[Dennis Jackson]

Attachment: Bug 1954724 - Prevent excess allocations in sslBuffer_Grow. r=#nss-reviewers

Comment 2

[Dennis Jackson]

https://hg.mozilla.org/projects/nss/rev/9cafa4c636a6f65cb09fd7e9f4b82f69897047ce