Hi Wolfgang,
On 04/28/2014 08:27 PM, w_schmidt@...181... wrote:
Hello,
I have a few question regarding genodes block cache in 14.02.
If understand it correctly on x86-based computers genode starts on top of linux.
well, that's not true. Yes, Genode is able to run on top of Linux, mostly for development purposes. But Genode runs also directly on x86 hardware using the NOVA kernel, or Fiasco.OC kernel, or the OKL4 kernel, or Pistachio kernel.
Therefore multiple caches will be used before something goes to genode a) the cache on a hdd b) cache on a drive controller c) the linux block cache
If running on Linux yes, but normally it wouldn't make much sense to use an additional block cache here.
d) qemu
As already said: you don't need to use Qemu. Most run scripts are starting Qemu by default, for convenience reasons only.
The first one is about the scenario in which the block cache is used. Is the block cache only thought for embedded devices where genode runs nativly? Are all embeded devices usable with the cache?
The block cache uses the block session of Genode. It uses exactly one block device, and serves exectly one client. As all block device drivers of Genode are implementing the block session interface, the block cache can be used on top of all block drivers, whether its a x86 AHCI driver, or MMC card driver of an ARM SoC, or whatever.
Is there a way to mount a partition in genode with qemu without using caches from c) and d) ? Or is there a x86 hardware where genode can directly operate on?
Qemu allows to define the caching policy of a hard drive (cache=none). I don't know whether it's possible to circumvent Linux block cache. I assume that's hard. But as mentioned above, you can use conventional x86 PC hardware.
Regards Stefan
As far as I have seen so far the disc cache of Linux does not seem to be disablable. I have only foudn ways to flush linux cache (like sync && echo 3
/proc/sys/vm/drop_caches).
Best regards, Wolfgang
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