[openib-general] Re: Re: [PATCH] TX/RX_RING_SIZE as loadable parameters

[Michael S. Tsirkin]

Quoting r. Talpey, Thomas <Thomas.Talpey at netapp.com>:
> Subject: Re: Re: [PATCH] TX/RX_RING_SIZE as loadable parameters
> 
> At 02:11 AM 3/7/2006, Michael S. Tsirkin wrote:
> >> The default TX_RING_SIZE is 64, RX_RING_SIZE is 128 in IPoIB, which 
> 
> >These parameters must be a power of 2, and at least 2, otherwise things
> >break. I'd suggest making these a log and multiplying the result by 2,
> >to exclude the possibility of user error.
> 
> Surely this isn't true of all hardware.

This is true for all hardware.
We have code in ipoib like
	tx_req = &priv->tx_ring[priv->tx_head & (IPOIB_TX_RING_SIZE - 1)]

So it only works for tz size that is a power of 2.

> If the underlying hardware requires a
> power of 2, it should fix it, not make a requirement on the framework setting?

Supporting arbitrary ring size will require integer division or
coditional code on data path, I don't think it's worth it.

-- 
Michael S. Tsirkin
Staff Engineer, Mellanox Technologies