On 07/23/2010 01:02 PM, Stefan Hajnoczi wrote:
>> In fact, we solve this problem through a really simple method.
>> In our prototype, we removed this piece of code like this:
>> void *qemu_get_ram_ptr(ram_addr_t addr)
>> {
>> ......
>>
>> /* Move this entry to to start of the list. */
>> #ifndef CONFIG_COREMU
>> /* Different core can access this function at the same time.
>> * For coremu, disable this optimization to avoid data race.
>> * XXX or use spin lock here if performance impact is big. */
>> if (prev) {
>> prev->next = block->next;
>> block->next = *prevp;
>> *prevp = block;
>> }
>> #endif
>> return block->host + (addr - block->offset);
>> }
>>
>> CONFIG_COREMU is defined when TCG parallel mode is configured.
>> And the list is more likely to be read only without hotplug device, so
>> we don't use a lock to protect it.
>> Reimplement this list with a lock free list is also reasonable, but
>> seems unnecessary. :-)
>
> Ah, good :).
For this one in particular, you could just use circular lists (without a
"head" node, unlike the Linux kernel's list data type, as there's always
a RAM entry) and start iteration at "prev".
Paolo
