RE: [Pv-drivers] [PATCH] vmxnet3: round down # of queues to power of two

I just want to point out that rounddown_pow_of_two() returns 0 when (1) the input is 1; and (2) the __buildin_constant_p(n) path is taken.  In the vmxnet3 case, even if num_rx_queues is 1, we are safe as its value is not known to be constant at compile time and 1 will be returned by taking the other path (1UL << (fls_long(n) - 1)). The original check of power_of_two is there just to be on the safe side.

Related to this, I wonder if we should always return 1 when the input is 1 (1 is also a power of two as 2^0). I don't have the history of this API though and curious if there are any users of this API that depend on this behavior?

Thanks,
Yong

-----Original Message-----
From: Dmitry Torokhov [mailto:dtor@vmware.com]
Sent: Wednesday, July 06, 2011 6:09 PM
To: pv-drivers@vmware.com
Cc: Shreyas Bhatewara; netdev@vger.kernel.org; Yong Wang
Subject: Re: [Pv-drivers] [PATCH] vmxnet3: round down # of queues to power of
two

On Wednesday, July 06, 2011 05:58:51 PM Shreyas Bhatewara wrote:

quoted

+	if (!is_power_of_2(num_rx_queues))
+		num_rx_queues = rounddown_pow_of_two(num_rx_queues);
+

No need to do the check, just do:

	num_rx_queues = rounddown_pow_of_two(num_rx_queues);

Thanks,
Dmitry