On Nov 19, 2013, at 11:11 AM, David F. <df7...@gmail.com> wrote:
> breaking it up to 512K size reads (256 sectors) did work - slower than
> I thought it would be
A CD-ROM has 2K block size, so maybe the driver is not caching and reading the
same block more than one time?
Thanks,
Andrew Fish
> but works. Thanks.
>
> On Tue, Nov 19, 2013 at 8:09 AM, Brian J. Johnson <bjohn...@sgi.com> wrote:
>> FWIW, we saw similar problems with a 3rd party SAS driver as well. It
>> provided only the BLOCK_IO protocol, and would error out if asked to
>> perform a read of 0x8000 or more blocks (16MB.) That broke a particular
>> version of Microsoft's boot loader, and there was nothing we could do
>> about it in our BIOS.
>>
>> So it sounds like this sort of problem is widespread.
>>
>> Brian Johnson
>>
>> On 11/19/2013 03:10 AM, Mike Maslenkin wrote:
>>> And we saw similar problems too.
>>>
>>> In our case the problem was in large PIO transfers.
>>> Since edk2 code base uses PIO for ATAPI devices, we are unable to handle
>>> such reads in our VM, because we have a 1MB bounce buffer for PIO.
>>>
>>> There were two solutions implemented:
>>> 1. We have added DMA support.
>>> 2. We have limited maximum transfer size for all block devices to 1 MB
>>> (in ScsiDiskDxe).
>>> //
>>> // limit the data bytes that can be transferred by one Read(10) or
>>> Read(16) Command
>>> //
>>> if (!ScsiDiskDevice->Cdb16Byte) {
>>> - MaxBlock = 0xFFFF;
>>> + MaxBlock = 0x200; // 1mb
>>> } else {
>>> MaxBlock = 0xFFFFFFFF;
>>> }
>>>
>>> The second solution is not so good, and I started to think about
>>> splitting request at
>>> AtaAtapiPassThruDxe, before submitting it to ATA device.
>>>
>>> Hope it helps.
>>>
>>> On Mon, 2013-11-18 at 19:35 -0800, H. Peter Anvin wrote:
>>>> On 11/18/2013 05:47 PM, David F. wrote:
>>>>> Thanks - I found the grub option for set debug= (I couldn't use all
>>>>> since it would lock up - but used disk,efidisk,modules,loader) and can
>>>>> see it reads 0x100 sectors from sector 0x500 then reads 0x4C00 sectors
>>>>> from sector 0x600. So perhaps that's it. Yes, legacy reads in the
>>>>> same inirmfs.gz file (which occupies 0x5AF to 0x525C) but I'm sure it
>>>>> does it in smaller chunks.
>>>>
>>>> We saw similar problems with extremely large reads while developing the
>>>> Linux EFI boot stub. We ended up capping the size of any one read call
>>>> to 1 MB. Sad but true.
>>>>
>>>> -hpa
>>>>
>>
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