On Thu, Aug 9, 2012 at 4:24 PM, Avi Kivity <avi@xxxxxxxxxx> wrote: > On 08/09/2012 10:28 AM, liu ping fan wrote: >>> >>> Seems to me that nothing in memory.c can susceptible to races. It must >>> already be called under the big qemu lock, and with the exception of >>> mutators (memory_region_set_*), changes aren't directly visible. >>> >> Yes, what I want to do is "prepare unplug out of protection of global >> lock". When io-dispatch and mmio-dispatch are all out of big lock, we >> will run into the following scene: >> In vcpu context A, qdev_unplug_complete()-> delete subregion; >> In context B, write pci bar --> pci mapping update -> add subregion > > Why do you want unlocked unplug? Unplug is rare and complicated; there > are no performance considerations on one hand, and difficulty of testing > for lock correctness on the other. I think it is better if it remains > protected by the global lock. > Oh, yes! I deviate quite far from the origin aim, and introduce some unnecessary complicate. >> >>> I think it's sufficient to take the mem_map_lock at the beginning of >>> core_begin() and drop it at the end of core_commit(). That means all >>> updates of volatile state, phys_map, are protected. >>> >> The mem_map_lock is to protect both address_space_io and >> address_space_memory. When without the protection of big lock, >> competing will raise among the updaters >> (memory_region_{add,del}_subregion and the readers >> generate_memory_topology()->render_memory_region(). > > These should all run under the big qemu lock, for the same reasons. > They are rare and not performance sensitive. Only phys_map reads are > performance sensitive. > OK, I see. Leave the big lock as it is, except for mmio, we will not worry about it. >> >> If just in core_begin/commit, we will duplicate it for >> xx_begin/commit, right? > > No. Other listeners will be protected by the global lock. > Yes, if leave the big lock as it is. >> And at the same time, mr->subregions is >> exposed under SMP without big lock. >> > > Who accesses it? > Again, I assume the updaters out of the protection of the big lock > IMO locking should look like: > > phys_map: mem_map_lock > dispatch callbacks: device specific lock (or big qemu lock for > unconverted devices) > everything else: big qemu lock > I See. Thank you for the review. And I will eliminate the unnecessary complicate and effort for the next version Regards, pingfan > > > -- > error compiling committee.c: too many arguments to function -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html