On 10/7/24 07:48, Michael Tokarev wrote:
23.10.2023 05:40, Song Gao wrote:
The LoongArch kernel supports 4K page size.
Change TARGET_PAGE_BITS to 12.
This change appears to have 2 issues.
First, the subject is misleading, - it does not only introduces support for 4K
page
size, it actually *switches* to 4K page size. But this is sort of minor.
More interestingly is that it has quite noticeable effect on performance. For
example, https://gitlab.com/qemu-project/qemu/-/issues/2491 - I confirm 7z
decompression performance drop from ~110Mb/s before this change to ~73Mb/s
after it.
Is such a performance drop expected?
The #2491 issue appears to be for user-mode emulation. Because the reported host is x86,
I would expect guest page size == host page size to improve performance, not degrade it.
If this were system mode emulation, quite possibly. If the guest loongarch kernel is
still using 16k pages, then all pages that are given to softmmu are "large pages", which
perform poorly. I hope to address this at some point.
If this is really about user-mode, then perf may be your friend in determining where the
extra overhead is coming from.
r~
