On Wed, 26 May 2021 15:51:42 +0800 Feng zhou <zhoufeng.zf@xxxxxxxxxxxxx> wrote: > From: ZHOUFENG <zhoufeng.zf@xxxxxxxxxxxxx> > > When we do the kernel monitor, use the DRGN > (https://github.com/osandov/drgn) access to kernel data structures, > found that the system calls a lot. DRGN is implemented by reading > /proc/kcore. After looking at the kcore code, it is found that kcore > does not implement mmap, resulting in frequent context switching > triggered by read. Therefore, we want to add mmap interface to optimize > performance. Since vmalloc and module areas will change with allocation > and release, consistency cannot be guaranteed, so mmap interface only > maps KCORE_TEXT and KCORE_RAM. > > The test results: > 1. the default version of kcore > real 11.00 > user 8.53 > sys 3.59 > > % time seconds usecs/call calls errors syscall > ------ ----------- ----------- --------- --------- ---------------- > 99.64 128.578319 12 11168701 pread64 > ... > ------ ----------- ----------- --------- --------- ---------------- > 100.00 129.042853 11193748 966 total > > 2. added kcore for the mmap interface > real 6.44 > user 7.32 > sys 0.24 > > % time seconds usecs/call calls errors syscall > ------ ----------- ----------- --------- --------- ---------------- > 32.94 0.130120 24 5317 315 futex > 11.66 0.046077 21 2231 1 lstat > 9.23 0.036449 177 206 mmap > ... > ------ ----------- ----------- --------- --------- ---------------- > 100.00 0.395077 25435 971 total > > The test results show that the number of system calls and time > consumption are significantly reduced. > hm, OK, I guess why not. The performance improvements for DRGN (which appears to be useful) are nice and the code is simple. I'm surprised that it makes this much difference. Has DRGN been fully optimised to minimise the amount of pread()ing which it does? Why does it do so much reading? Thanks, I shall await input from others before moving ahead with this.
