(2012/07/24 11:36), Yoshihiro YUNOMAE wrote: > Therefore, we propose a new system "virtio-trace", which uses enhanced > virtio-serial and existing ring-buffer of ftrace, for collecting guest kernel > tracing data. In this system, there are 5 main components: > (1) Ring-buffer of ftrace in a guest > - When trace agent reads ring-buffer, a page is removed from ring-buffer. > (2) Trace agent in the guest > - Splice the page of ring-buffer to read_pipe using splice() without > memory copying. Then, the page is spliced from write_pipe to virtio > without memory copying. > (3) Virtio-console driver in the guest > - Pass the page to virtio-ring > (4) Virtio-serial bus in QEMU > - Copy the page to kernel pipe > (5) Reader in the host > - Read guest tracing data via FIFO(named pipe)
So, this is our answer for the argued points in previous thread. This virtio-serial and ftrace enhancements doesn't introduce new "ringbuffer" in the kernel, and just use virtio's ringbuffer. Also, using splice gives us a great advantage in the performance because of copy-less trace-data transfer. Actually, one copy should occur in the host (to write it into the pipe), because removing physical pages of the guest is hard to track and may involve a TLB flush per page, even if it is done in background. Thank you, -- Masami HIRAMATSU Software Platform Research Dept. Linux Technology Center Hitachi, Ltd., Yokohama Research Laboratory E-mail: masami.hiramatsu...@hitachi.com
