Hi all,
I've recently installed Debian Jessie 64-bit on my (admittedly rather
old) dual Opteron workstation, and I'm experiencing pretty bad
performance in X11. Certain redrawing operations are extremely slow,
with delays of half a second or more, and Xorg consumes a lot of CPU
time. I've wondered if it's particularly a problem for older X clients
using bitmapped fonts, as it's very noticeable when running xosview and
when dragging tabs and invoking menus in Notion (window manager), but
menu drawing in GIMP is also very slow. The machine has 8 GiB of RAM
and only a couple are being used. It was formerly running Ubuntu 12 LTS
and didn't have this problem.
`Xorg -version` reports the following:
X.Org X Server 1.16.4
Release Date: 2014-12-20
X Protocol Version 11, Revision 0
Build Operating System: Linux 3.16.0-4-amd64 x86_64 Debian
Current Operating System: Linux zaphod 3.16.0-4-amd64 #1 SMP Debian
3.16.7-ckt11-1 (2015-05-24) x86_64
Kernel command line: BOOT_IMAGE=/boot/vmlinuz-3.16.0-4-amd64
root=UUID=2cd952af-5971-442e-9254-bb15730dec1a ro quiet
Build Date: 11 February 2015 12:32:02AM
xorg-server 2:1.16.4-1 (http://www.debian.org/support)
Current version of pixman: 0.32.6
My video card is a Radeon X800 XT Platinum Edition AGP, and Xorg is
using the RADEON driver. It's running in dual-head mode.
`perf top` seems to indicate that the C library's memcpy implementation
is the main culprit:
44.29% libc-2.19.so [.] __memcpy_sse2_unaligned
Here's the disassembly of the same, also courtesy of `perf`:
<<
__memcpy_sse2_unaligned /lib/x86_64-linux-gnu/libc-2.19.so
...
│ lea 0x30(%r10),%rax
▒
│ movdqu (%rcx,%r10,1),%xmm8
▒
10.42 │ movdqa %xmm8,(%rcx)
▒
5.03 │ movdqu (%rcx,%r9,1),%xmm8
▒
10.35 │ movdqa %xmm8,0x10(%rcx)
▒
10.60 │ movdqu (%rcx,%r8,1),%xmm8
▒
14.00 │ movdqa %xmm8,0x20(%rcx)
▒
7.87 │ movdqu (%rcx,%rax,1),%xmm8
▒
12.53 │ movdqa %xmm8,0x30(%rcx)
▒
7.57 │ add $0x40,%rcx
▒
│ cmp %rcx,%rdx
▒
10.08 │ ↓ jne 780
▒
│ ↓ jmpq 6de
▒
│ cmp %rsi,%rdi
>>
Could it be a performance regression due to recent enhancements to GLIBC
for newer CPUs? Any thoughts on how I can test this further?
Thanks,
Chris
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