The method to alloc DMA ring buffer

[Tony He]

Thanks! Gained a lot.

Tom Mitchell <niftylinkern at niftyegg.com> 于2022年12月8日周四 03:55写道：
>
> On Tue, Dec 6, 2022 at 8:17 PM Tony He <huangya90 at gmail.com> wrote:
> ...
> >
> > I'm studying the NIC driver with the book <<Understanding the linux
> > network internals>>. This book uses 3com 3c59x NIC(3c59x.c) as an
> > example. The driver is very old and few people discuss it, but it's a
> > good place to start because it's simpler than many other drivers with
> > advanced offload features.
> >
> > In the interrupt handler boomerang_rx(), I see it pre-allocate one new
> ...
>
> >     goto clear_complete;
> Oh m a goto.
> ...
> > However, I see intel e1000 driver optimizes this. Intel doesn't
> > pre-allocate one at a time.
> ....
> > I just want to know why this is faster. For all scenarios or some
> > scenarios? Can someone analyse it rigorously?
>
> The first step is to examine the hardware data pages.
> Most optimizations like this are shaped by hardware
>
> That said, buffer allocation in the kernel is slow(ish).
> Any time there is sufficient ram to preallocate, do so in moderation.
> ...
> Interrupt latency.
> It helps to have the hardware address a list of commands in a queue without
> hardware intervention.
> Networking:
> a buffer window sent to the client  allows that client to send data
> without waiting on
> a response and is unlikely to need to resend unless the network has loss.
>
> The networking buffer window strategy is a giant topic.
>
> Interrupt latency: that is another book  and it depends on the hardware.  Again
> any hardware that can do useful work without interrupt servicing the better.
>
> Simple serial IO hardware drivers can be easier to research and analyze.
> Again start with the hardware data sheets for UARTS and hardware and software
> flow control over serial data links.
>
> Define: rigorously?  Is this a homework assignment?
No, this is NOT a homework assignment. Have worked a few years but my
most areas were related to application instead
of kernel and driver.