Re: [Qemu-devel] [PATCH v3 2/5] util: introduce threaded workqueue

[Xiao Guangrong]

On 11/23/18 7:02 PM, Dr. David Alan Gilbert wrote:

> > +#include "qemu/osdep.h"
> > +#include "qemu/bitmap.h"
> > +#include "qemu/threaded-workqueue.h"
> > +
> > +#define SMP_CACHE_BYTES 64
>
> That's architecture dependent isn't it?

Yes, it's arch dependent indeed.

I just used 64 for simplification and i think it is <= 64 on most CPU arch-es
so that can work.

Should i introduce statically defined CACHE LINE SIZE for all arch-es? :(

> > +   /*
> > +     * the bit in these two bitmaps indicates the index of the ＠requests
> > +     * respectively. If it's the same, the corresponding request is free
> > +     * and owned by the user, i.e, where the user fills a request. Otherwise,
> > +     * it is valid and owned by the thread, i.e, where the thread fetches
> > +     * the request and write the result.
> > +     */
> > +
> > +    /* after the user fills the request, the bit is flipped. */
> > +    uint64_t request_fill_bitmap QEMU_ALIGNED(SMP_CACHE_BYTES);
> > +    /* after handles the request, the thread flips the bit. */
> > +    uint64_t request_done_bitmap QEMU_ALIGNED(SMP_CACHE_BYTES);
>
> Patchew complained about some type mismatches; I think those are because
> you're using the bitmap_* functions on these; those functions always
> operate on 'long' not on uint64_t - and on some platforms they're
> unfortunately not the same.

I guess you were taking about this error:
ERROR: externs should be avoided in .c files
#233: FILE: util/threaded-workqueue.c:65:
+    uint64_t request_fill_bitmap QEMU_ALIGNED(SMP_CACHE_BYTES);

The complained thing is "QEMU_ALIGNED(SMP_CACHE_BYTES)" as it gone
when the aligned thing is removed...

The issue you pointed out can be avoid by using type-casting, like:
bitmap_xor(..., (void *)&thread->request_fill_bitmap)
cannot we?

Thanks!