Re: Making Lemonade (Floating-point format changes)

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Sujet : Re: Making Lemonade (Floating-point format changes)
De : mitchalsup (at) *nospam* aol.com (MitchAlsup1)
Groupes : comp.arch
Date : 17. May 2024, 01:10:48
Autres entêtes
Organisation : Rocksolid Light
Message-ID : <06ca70b0f9a7f44c59dd827779ad855e@www.novabbs.org>
References : 1 2 3 4 5 6 7 8 9 10 11 12 13
User-Agent : Rocksolid Light
EricP wrote:

MitchAlsup1 wrote:
Scott Lurndal wrote:
 
mitchalsup@aol.com (MitchAlsup1) writes:
BGB wrote:
 
Also I may need to rework how page-in/page-out is handled (and or how IO is handled in general) since if a page swap needs to happen while IO is already in progress (such as a page-miss in the system-call process), at present, the OS is dead in the water (one can't access the SDcard in the middle of a different access to the SDcard).
>
Having a HyperVisor helps a lot here, with HV taking the page faults
of the OS page fault handler.
>
Seems like adding another layer couldn't help with this, unless it also abstracts away the SDcard interface.
>
With a HV, GuestOS does not "do" IO is paravirtualizes it via HV.
 
Actually, that's not completely accurate.  With PCI Express SR-IOV,
an I/O MMU and hardware I/O virtualization, the guest accesses the I/O device
hardware directly and initiates DMA transactions to-or-from the
guest OS directly.   With the PCIe PRI (Page Request Interface), the
guest DMA target pages don't need to be pinned by the hypervisor; the
I/O MMU will interrupt the hypervisor to make the page present
and pin it and the hardware will then do the DMA.
 This was something I was not aware of but probably should have anticipated.
 GuestOS initiates an I/O request (command) using a virtual function.
Rather than going through a bunch of activities to verify the user
owns the page and it is present, GuestOS just launches request and
then the I/O device page faults and pins the required page (if it is
not already so)--much like the page fault volcano when a new process
begins running:: page faulting in .text, the stack, and data pages
as they get touched.
 This way, GuestOS simply considers all pages in its "portfolio" to be
present in memory, and HV does the heavy lifting and page virtualization.
 I guess I should have anticipated this. Sorry !!

The reason OS's pin the pages before the IO starts is so there is no
latency reading in from a device, which then has to buffer the input.
An HDD seek avg about 9 ms, add 3 ms for the page fault code.
A 100 Mbs Ethernet can receive 10 MB/s or 10 kB/ms, = 120 kB in 12 ms.

What would likely happen is the Ethernet card buffer would fill up
then it starts tossing packets, while it waits for HV to page fault
the receive buffer in from its page file. Later when the guest OS
buffer has faulted in and the card's buffer is emptied, the network
software will eventually NAK all the tossed packets and they get resent.

So there is a stutter every time the HV recycles that guest OS memory
that requires retransmissions to fix. And this is basically using the
senders memory to buffer the transmission while this HV page faults.

Note there are devices, like A to D converters which cannot fix the
tossed data by asking for a retransmission. Or devices like tape drives
which can rewind and reread but are verrry slow about it.

I would want an option in this SR-IOV mechanism for the guest app to
tell the guest OS to tell the HV to pin the buffer before starting IO.
So, what happens if GuestOS thinks the user file is located on a local
SATA drive, but it is really across some network ?? This works when devices are not virtualized since the request is routed to a different
system where the file is local, accessed and data returned over the
network.
Does this mean the application has lost a level of indirection in order
to have become virtualized ?????

Date Sujet#  Auteur
12 May 24 * Making Lemonade (Floating-point format changes)101John Savard
12 May 24 +* Re: Making Lemonade (Floating-point format changes)3wolfgang kern
15 May 24 i`* Re: Making Lemonade (Floating-point format changes)2Michael S
15 May 24 i `- Re: Making Lemonade (Floating-point format changes)1BGB
12 May 24 +* Re: Making Lemonade (Floating-point format changes)6Thomas Koenig
12 May 24 i`* Re: Making Lemonade (Floating-point format changes)5John Savard
12 May 24 i +- Re: Making Lemonade (Floating-point format changes)1John Savard
12 May 24 i `* Re: Making Lemonade (Floating-point format changes)3MitchAlsup1
13 May 24 i  `* Re: Making Lemonade (Floating-point format changes)2John Savard
13 May 24 i   `- Re: Making Lemonade (Floating-point format changes)1BGB
12 May 24 `* Re: Making Lemonade (Floating-point format changes)91John Dallman
12 May 24  `* Re: Making Lemonade (Floating-point format changes)90Thomas Koenig
13 May 24   `* Re: Making Lemonade (Floating-point format changes)89Michael S
13 May 24    +* Re: Making Lemonade (Floating-point format changes)56Thomas Koenig
14 May 24    i`* Re: Making Lemonade (Floating-point format changes)55Michael S
15 May 24    i `* Re: Making Lemonade (Floating-point format changes)54Thomas Koenig
15 May 24    i  `* Re: Making Lemonade (Floating-point format changes)53Michael S
19 May 24    i   `* Re: Making Lemonade (Floating-point format changes)52Thomas Koenig
19 May 24    i    +* Re: Making Lemonade (Floating-point format changes)3Michael S
19 May 24    i    i+- Re: Making Lemonade (Floating-point format changes)1MitchAlsup1
20 May 24    i    i`- Re: Making Lemonade (Floating-point format changes)1Thomas Koenig
19 May 24    i    `* Re: Making Lemonade (Floating-point format changes)48Terje Mathisen
19 May 24    i     +* Re: Making Lemonade (Floating-point format changes)40Michael S
19 May 24    i     i+- Re: Making Lemonade (Floating-point format changes)1MitchAlsup1
20 May 24    i     i+* Re: Making Lemonade (Floating-point format changes)30Terje Mathisen
20 May 24    i     ii`* Re: Making Lemonade (Floating-point format changes)29Michael S
20 May 24    i     ii `* Re: Making Lemonade (Floating-point format changes)28Terje Mathisen
20 May 24    i     ii  `* Re: Making Lemonade (Floating-point format changes)27Michael S
20 May 24    i     ii   +* Re: Making Lemonade (Floating-point format changes)19BGB
20 May 24    i     ii   i`* Re: Making Lemonade (Floating-point format changes)18MitchAlsup1
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20 May 24    i     ii   i +- Re: Making Lemonade (Floating-point format changes)1Thomas Koenig
21 May 24    i     ii   i `* Re: Making Lemonade (Floating-point format changes)15BGB
21 May 24    i     ii   i  +* Re: Making Lemonade (Floating-point format changes)12Thomas Koenig
21 May 24    i     ii   i  i+* Re: Making Lemonade (Floating-point format changes)7Michael S
21 May 24    i     ii   i  ii+* Re: Making Lemonade (Floating-point format changes)5Terje Mathisen
21 May 24    i     ii   i  iii+- Re: Making Lemonade (Floating-point format changes)1Michael S
21 May 24    i     ii   i  iii`* Re: Making Lemonade (Floating-point format changes)3BGB
22 May 24    i     ii   i  iii `* Re: Making Lemonade (Floating-point format changes)2MitchAlsup1
22 May 24    i     ii   i  iii  `- Re: Making Lemonade (Floating-point format changes)1BGB-Alt
21 May 24    i     ii   i  ii`- Re: Making Lemonade (Floating-point format changes)1Thomas Koenig
21 May 24    i     ii   i  i`* Re: Making Lemonade (Floating-point format changes)4BGB
21 May 24    i     ii   i  i `* Re: Making Lemonade (Floating-point format changes)3MitchAlsup1
21 May 24    i     ii   i  i  +- Re: Making Lemonade (Floating-point format changes)1BGB
22 May 24    i     ii   i  i  `- Re: Making Lemonade (Floating-point format changes)1Terje Mathisen
21 May 24    i     ii   i  `* Re: Making Lemonade (Floating-point format changes)2MitchAlsup1
21 May 24    i     ii   i   `- Re: Making Lemonade (Floating-point format changes)1BGB
20 May 24    i     ii   `* Re: Making Lemonade (Floating-point format changes)7Terje Mathisen
21 May 24    i     ii    `* Re: Making Lemonade (Floating-point format changes)6Michael S
21 May 24    i     ii     `* Re: Making Lemonade (Floating-point format changes)5MitchAlsup1
21 May 24    i     ii      +* Re: Making Lemonade (Floating-point format changes)2Stefan Monnier
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22 May 24    i     ii      +- Re: Making Lemonade (Floating-point format changes)1Terje Mathisen
22 May 24    i     ii      `- Re: Making Lemonade (Floating-point format changes)1MitchAlsup1
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20 May 24    i     i `* Re: binary128 implementation7Terje Mathisen
23 May 24    i     i  `* Re: binary128 implementation6BGB-Alt
23 May 24    i     i   `* Re: binary128 implementation5MitchAlsup1
24 May 24    i     i    `* Re: binary128 implementation4Terje Mathisen
24 May 24    i     i     `* Re: binary128 implementation3BGB-Alt
25 May 24    i     i      `* Re: binary128 implementation2MitchAlsup1
25 May 24    i     i       `- Re: binary128 implementation1BGB
19 May 24    i     +* Re: Making Lemonade (Floating-point format changes)6BGB
19 May 24    i     i`* Re: Making Lemonade (Floating-point format changes)5MitchAlsup1
20 May 24    i     i `* Re: Making Lemonade (Floating-point format changes)4BGB
20 May 24    i     i  `* Re: Making Lemonade (Floating-point format changes)3MitchAlsup1
20 May 24    i     i   `* Re: Making Lemonade (Floating-point format changes)2BGB
20 May 24    i     i    `- Re: Making Lemonade (Floating-point format changes)1MitchAlsup1
19 May 24    i     `- Re: Making Lemonade (Floating-point format changes)1MitchAlsup1
13 May 24    `* Re: Making Lemonade (Floating-point format changes)32BGB
13 May 24     `* Re: Making Lemonade (Floating-point format changes)31MitchAlsup1
14 May 24      +* Re: Making Lemonade (Floating-point format changes)22BGB
14 May 24      i`* Re: Making Lemonade (Floating-point format changes)21MitchAlsup1
14 May 24      i `* Re: Making Lemonade (Floating-point format changes)20BGB
14 May 24      i  `* Re: Making Lemonade (Floating-point format changes)19MitchAlsup1
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15 May 24      i   i`- Re: Making Lemonade (Floating-point format changes)1Michael S
14 May 24      i   +- Re: Making Lemonade (Floating-point format changes)1BGB
16 May 24      i   `* Re: Making Lemonade (Floating-point format changes)15MitchAlsup1
17 May 24      i    `* Re: Making Lemonade (Floating-point format changes)14MitchAlsup1
17 May 24      i     +* Re: Making Lemonade (Floating-point format changes)2MitchAlsup1
18 May 24      i     i`- Re: Making Lemonade (Floating-point format changes)1MitchAlsup1
18 May 24      i     `* Re: Making Lemonade (Floating-point format changes)11Chris M. Thomasson
19 May 24      i      `* Re: Making Lemonade (Floating-point format changes)10Chris M. Thomasson
19 May 24      i       `* Re: Making Lemonade (Floating-point format changes)9Chris M. Thomasson
19 May 24      i        `* Re: Making Lemonade (Floating-point format changes)8Chris M. Thomasson
20 May 24      i         `* Re: Making Lemonade (Floating-point format changes)7Chris M. Thomasson
20 May 24      i          `* Re: Making Lemonade (Floating-point format changes)6Chris M. Thomasson
20 May 24      i           `* Re: Making Lemonade (Floating-point format changes)5Chris M. Thomasson
24 May 24      i            `* Re: Making Lemonade (Floating-point format changes)4Chris M. Thomasson
26 May 24      i             `* Re: Making Lemonade (Floating-point format changes)3George Neuner
27 May 24      i              +- Re: Making Lemonade (Floating-point format changes)1Chris M. Thomasson
1 Jun 24      i              `- Re: Making Lemonade (Floating-point format changes)1Chris M. Thomasson
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14 May 24      i`* Re: Making Lemonade (Floating-point format changes)3MitchAlsup1
14 May 24      i +- Re: Making Lemonade (Floating-point format changes)1MitchAlsup1
14 May 24      i `- Re: Making Lemonade (Floating-point format changes)1BGB
10 Jun 24      `* Re: Making Lemonade (Floating-point format changes)4Lawrence D'Oliveiro
10 Jun 24       `* Re: Making Lemonade (Floating-point format changes)3Terje Mathisen
10 Jun 24        `* Re: Making Lemonade (Floating-point format changes)2Niklas Holsti
11 Jun 24         `- Re: Making Lemonade (Floating-point format changes)1Lawrence D'Oliveiro

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