machine check

hb12112

兩個不同的外部設(shè)備同一時間對同一片內(nèi)存進入DMA操作會不會導致kernel machine check.

accessory

Sorry. I cannot type Chinese on this machine.

In theory, that situation (two devices write to the same memory at the same time) will never happen. For example, PCI bus supports bus mater mode, which is capable to DMA. In that mode, the bus is locked for that device only. So other device cannot do DMA at the same time.

PCI express is a little bit different. But I think the PCIE standard or the MCH (NORTH BRIDGE) will take care of it.

hb12112

謝謝你的回復。
我們用的是PCIE bus.
我們經(jīng)過測試發(fā)現(xiàn)，兩個設(shè)備同一時間DMA讀同一片內(nèi)存時發(fā)生machine check.
難道不允許這樣？

bluesea666

謝謝你的回復。
我們用的是PCIE bus.
我們經(jīng)過測試發(fā)現(xiàn)，兩個設(shè)備同一時間DMA讀同一片內(nèi)存時發(fā)生machine  ...
hb12112 發(fā)表于 2010-06-15 10:50

    應該是有限制吧.

hb12112

寫是為了保證數(shù)據(jù)一致性的話，讀為什么要限制呢？是內(nèi)核里限制還是由硬件保證？

accessory

It looks like a hardware mechanism. See following links:

http://en.wikipedia.org/wiki/Machine_Check_Exception
http://en.wikipedia.org/wiki/Machine_check_architecture

You can also try some tools to get the details about the machine check.

Solaris12

謝謝你的回復。
我們用的是PCIE bus.
我們經(jīng)過測試發(fā)現(xiàn)，兩個設(shè)備同一時間DMA讀同一片內(nèi)存時發(fā)生machine  ...
hb12112 發(fā)表于 2010-06-15 10:50

    兩個設(shè)備同時DMA同一片內(nèi)存當然是bug.

    有點好奇，你的兩個設(shè)備是在不同的root complex下嗎？

    另外你的機器enable IOMMU了嗎？

hb12112

由什么來保證兩個設(shè)備不在同一時間DMA?
兩個設(shè)備同時DMA讀同一片內(nèi)存有什么問題?
iommu是關(guān)閉的.

accessory

Good question.

I guess the PCIE bridge or NB (MCH) is in charge of controlling DMA. But I don't know why two DMA reads from two device cannot happen at the same time.

For PCI bus, it seems reasonable, because it is parallel bus and when one device control the bus, other device cannot have the same degree of control.
But PCI Express is serial bus so it may allow two device to do DMA read at the same time in theory?

帥絕人寰

>I guess the PCIE bridge or NB (

bridge 應該是root complex