Questions on network and block device related IRQ handling

[Shane Wayne <zx0319 at gmail dot com>]

Hi all:
I've recently doing some research on network and block device related
IRQ handling, so I use some database and network cache application as
the testbed.
I probed the following probes below:
netdev receive
netdev transmit
netdev hard_transmit
ioblock request
ioblock end

irq_handler.entry
irq_handler,exit
softirq.entry
softirq.exit

After the profiling, I notice that, when netdev receive is triggered.
It always appears within a softirq, and the softirq has a irq_handler
in front of it. It mean the sequence is like:

irq_handler.entry
irq_handler.exit
softirq.entry
    one or several netdev receive
softirq.exit

And I found that, the irq could happened in any process, even in my
application's context, but in most condition, it was found in swapper
process.

And when it comes to netdev transmit, it seems that this action do not
relate with irq? The sequence just happens in the application context.

netdev transmit begin
        netdev hard_transmit begin
        netdev hard_transmit end
netdev transmit end

And it doesn't use irq?

So here is my question:
1, it seems that irq_handler from network device just be responsible
to notify the package arrival, and the actual handling was done by the
following soft irq?

2, the irq handling seems could happen in any process, and do not stop
current context, but when the server is not heavily loaded, the irq
prefer to happen in swapper process?

3, Or just because the swapper take more cpu time when the server was
not heavily loaded?

4, does the netdev send or ioblock request really do not need irq's assistant?

5, if this is true, how could we determine when the netdev transmit
finish it's job? is the time of netdev hard_transmit end correct?

THX~

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ZHANG Xiao

The Institute of Computer Software Engineering and Theory in Xi'an
Jiaotong University
Master-and-Doctoral Program Student

ACM Student Member
CCF Student Member
IEEE Computer Society Sister Society Associate Member

Xi'an Jiaotong University
Bachelor of Engineering in Computer Science and Technology

The Chinese University of Hong Kong
International Asia Study Program in CS/CE/EE/IE