[Qemu-devel] Re: Release of COREMU, a scalable and portable full-system emulator

[Paolo Bonzini <pbonzini@redhat.com>]

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