Date: Wed, 4 May 2011 23:26:04 +0200 From: Jilles Tjoelker <jilles@stack.nl> To: John Baldwin <jhb@freebsd.org> Cc: arch@freebsd.org Subject: Re: [PATCH] Add ktrace records for user page faults Message-ID: <20110504212604.GA13717@stack.nl> In-Reply-To: <201105021537.19507.jhb@freebsd.org> References: <201105021537.19507.jhb@freebsd.org>
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On Mon, May 02, 2011 at 03:37:19PM -0400, John Baldwin wrote: > One thing I have found useful is knowing when processes are in the > kernel instead of in userland. ktrace already provides records for > syscall entry/exit. The other major source of time spent in the > kernel that I've seen is page fault handling. To that end, I have a > patch that adds ktrace records to the beginning and end of VM faults. > This gives a pair of records so a user can see how long a fault took > (similar to how one can see how long a syscall takes now). Sample > output from kdump is below: > 47565 echo CALL mmap(0x800a87000,0x179000,PROT_READ| > PROT_WRITE,MAP_PRIVATE|MAP_ANON,0xffffffff,0) > 47565 echo RET mmap 34370777088/0x800a87000 > 47565 echo PFLT 0x800723000 VM_PROT_EXECUTE > 47565 echo RET KERN_SUCCESS > 47565 echo CALL munmap(0x800887000,0x179000) > 47565 echo RET munmap 0 > 47565 echo PFLT 0x800a00000 VM_PROT_WRITE > 47565 echo RET KERN_SUCCESS Just a small nitpick, I think the return from a page fault should not use the same "RET" keyword; even though the next word unambiguously distinguishes it from a return from a syscall, I think it is clearer in the documentation and possibly useful for automated processing to use a separate keyword such as "PRET". -- Jilles Tjoelker
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