• Srinivasa D S's avatar
    kprobes: improve kretprobe scalability with hashed locking · ef53d9c5
    Srinivasa D S authored
    Currently list of kretprobe instances are stored in kretprobe object (as
    used_instances,free_instances) and in kretprobe hash table.  We have one
    global kretprobe lock to serialise the access to these lists.  This causes
    only one kretprobe handler to execute at a time.  Hence affects system
    performance, particularly on SMP systems and when return probe is set on
    lot of functions (like on all systemcalls).
    
    Solution proposed here gives fine-grain locks that performs better on SMP
    system compared to present kretprobe implementation.
    
    Solution:
    
     1) Instead of having one global lock to protect kretprobe instances
        present in kretprobe object and kretprobe hash table.  We will have
        two locks, one lock for protecting kretprobe hash table and another
        lock for kretporbe object.
    
     2) We hold lock present in kretprobe object while we modify kretprobe
        instance in kretprobe object and we hold per-hash-list lock while
        modifying kretprobe instances present in that hash list.  To prevent
        deadlock, we never grab a per-hash-list lock while holding a kretprobe
        lock.
    
     3) We can remove used_instances from struct kretprobe, as we can
        track used instances of kretprobe instances using kretprobe hash
        table.
    
    Time duration for kernel compilation ("make -j 8") on a 8-way ppc64 system
    with return probes set on all systemcalls looks like this.
    
    cacheline              non-cacheline             Un-patched kernel
    aligned patch 	       aligned patch
    ===============================================================================
    real    9m46.784s       9m54.412s                  10m2.450s
    user    40m5.715s       40m7.142s                  40m4.273s
    sys     2m57.754s       2m58.583s                  3m17.430s
    ===========================================================
    
    Time duration for kernel compilation ("make -j 8) on the same system, when
    kernel is not probed.
    =========================
    real    9m26.389s
    user    40m8.775s
    sys     2m7.283s
    =========================
    Signed-off-by: default avatarSrinivasa DS <srinivasa@in.ibm.com>
    Signed-off-by: default avatarJim Keniston <jkenisto@us.ibm.com>
    Acked-by: default avatarAnanth N Mavinakayanahalli <ananth@in.ibm.com>
    Cc: Anil S Keshavamurthy <anil.s.keshavamurthy@intel.com>
    Cc: David S. Miller <davem@davemloft.net>
    Cc: Masami Hiramatsu <mhiramat@redhat.com>
    Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
    Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
    ef53d9c5
kprobes.c 29.7 KB