|
From: | Taylor Simpson |
Subject: | Known issue? qemu is much slower when built with clang vs gcc |
Date: | Mon, 24 Aug 2020 16:54:01 +0000 |
We’re seeing significant slowdowns when we build qemu with clang instead of gcc. I’m hoping this is a known issue and there is a workaround or fix. Please advise. I have an example where qemu is 29X slower when built with clang. My first hunch was that there was something different happening in configure (e.g., passing -O0 to clang instead of -O2). However, I have ruled this out. Further investigation shows that we are calling the translator more often. The same code is getting translated multiple times. So, my current theory is some different behavior in the translation block hashing causing the lookup not to
find existing translations. I know clang can be overly aggressive about optimizing undefined behavior. So, I turned on clang’s undefined behavior sanitizer. Interestingly, it did not report anything, *and* we don’t see the large performance difference. Thanks, Taylor |
[Prev in Thread] | Current Thread | [Next in Thread] |