52/66: programming-2022: Clarify QEMU options, as suggested by reviewers.

[Ludovic Courtès]

civodul pushed a commit to branch master
in repository maintenance.

commit b8c7505ee9f1f4cb5abbbb0564c93ce25a110122
Author: Ludovic Courtès <ludo@gnu.org>
AuthorDate: Thu Apr 28 13:50:45 2022 +0200

    programming-2022: Clarify QEMU options, as suggested by reviewers.
    
    * doc/programming-2022/artifact/README.md: Clarify QEMU option and the
    impact on the performance claim.
---
 doc/programming-2022/artifact/README.md | 21 +++++++++++++++++++--
 1 file changed, 19 insertions(+), 2 deletions(-)

diff --git a/doc/programming-2022/artifact/README.md 
b/doc/programming-2022/artifact/README.md
index 1c81dea..2a16fa6 100644
--- a/doc/programming-2022/artifact/README.md
+++ b/doc/programming-2022/artifact/README.md
@@ -21,7 +21,7 @@ system to retrieve and authenticate the image:
 ```
 wget -O /tmp/qemu-image \
   https://ftp.gnu.org/gnu/guix/guix-system-vm-image-1.3.0.x86_64-linux.qcow2
-wget -O /tmp/qemu-image.sig
+wget -O /tmp/qemu-image.sig \
   
https://ftp.gnu.org/gnu/guix/guix-system-vm-image-1.3.0.x86_64-linux.qcow2.sig
 wget https://sv.gnu.org/people/viewgpg.php?user_id=127547 \
   -qO - | gpg --import -
@@ -29,7 +29,8 @@ gpg --verify /tmp/qemu-image.sig
 ```
 
 You can then spawn the VM, using [QEMU](https://qemu.org) (with network
-access and at least 2 GiB or RAM):
+access, as specified with `-nic`, and at least 2 GiB of RAM, as
+specified with `-m`):
 
 ```
 qemu-system-x86_64 \
@@ -39,6 +40,18 @@ qemu-system-x86_64 \
   -drive if=none,file=/tmp/qemu-image,id=myhd
 ```
 
+> Note: We highly recommend running this on an x86_64 machine (64-bit
+> AMD/Intel processor); running it from another architecture would incur
+> significant run-time overhead.
+>
+> Furthermore, when using QEMU on GNU/Linux, the `-enable-kvm` switch
+> instructs QEMU to use the [KVM virtualization
+> mechanism](https://www.linux-kvm.org), which allows it to run code
+> with very little overhead compared to native code.  You can omit the
+> `-enable-kvm` option (for example if KVM is not supported on your
+> machine or if you are not running GNU/Linux), but be aware that
+> emulation without KVM will be much slower.
+
 Please see the installation instructions mentioned above for more
 information.
 
@@ -102,6 +115,10 @@ Section 8.3 of the paper.
 The performance claim can also be verified by running `guix git
 authenticate` as will be shown below.
 
+> Note: To verify the performance claim, you must be running QEMU on an
+> x86_64 machine and with `-enable-kvm` flag.  Failing to do that, the
+> emulation overhead will be prohibitively high.
+
 ## Commit Authentication
 
 **Claim: `guix pull` authenticates commits.**