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Tsirkin" , peterx@redhat.com, Alex Williamson , Jason Wang , Bandan Das , Prasad Pandit , Fabiano Rosas Subject: [PATCH 05/10] docs/migration: Split "Debugging" and "Firmware" Date: Tue, 9 Jan 2024 14:46:23 +0800 Message-ID: <20240109064628.595453-6-peterx@redhat.com> In-Reply-To: <20240109064628.595453-1-peterx@redhat.com> References: <20240109064628.595453-1-peterx@redhat.com> MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable X-Scanned-By: MIMEDefang 3.4.1 on 10.11.54.9 Received-SPF: pass (zohomail.com: domain of gnu.org designates 209.51.188.17 as permitted sender) client-ip=209.51.188.17; envelope-from=qemu-devel-bounces+importer=patchew.org@nongnu.org; helo=lists.gnu.org; Received-SPF: pass client-ip=170.10.129.124; envelope-from=peterx@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -43 X-Spam_score: -4.4 X-Spam_bar: ---- X-Spam_report: (-4.4 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-2.243, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H4=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001, T_SCC_BODY_TEXT_LINE=-0.01 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+importer=patchew.org@nongnu.org Sender: qemu-devel-bounces+importer=patchew.org@nongnu.org X-ZohoMail-DKIM: pass (identity @redhat.com) X-ZM-MESSAGEID: 1704782851420100014 Content-Type: text/plain; charset="utf-8" From: Peter Xu Move the two sections into a separate file called "best-practises.rst". Add the entry into index. Signed-off-by: Peter Xu Reviewed-by: C=C3=A9dric Le Goater --- docs/devel/migration/best-practises.rst | 48 +++++++++++++++++++++++++ docs/devel/migration/index.rst | 1 + docs/devel/migration/main.rst | 44 ----------------------- 3 files changed, 49 insertions(+), 44 deletions(-) create mode 100644 docs/devel/migration/best-practises.rst diff --git a/docs/devel/migration/best-practises.rst b/docs/devel/migration= /best-practises.rst new file mode 100644 index 0000000000..ba122ae417 --- /dev/null +++ b/docs/devel/migration/best-practises.rst @@ -0,0 +1,48 @@ +=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D +Best practises +=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D + +Debugging +=3D=3D=3D=3D=3D=3D=3D=3D=3D + +The migration stream can be analyzed thanks to ``scripts/analyze-migration= .py``. + +Example usage: + +.. code-block:: shell + + $ qemu-system-x86_64 -display none -monitor stdio + (qemu) migrate "exec:cat > mig" + (qemu) q + $ ./scripts/analyze-migration.py -f mig + { + "ram (3)": { + "section sizes": { + "pc.ram": "0x0000000008000000", + ... + +See also ``analyze-migration.py -h`` help for more options. + +Firmware +=3D=3D=3D=3D=3D=3D=3D=3D + +Migration migrates the copies of RAM and ROM, and thus when running +on the destination it includes the firmware from the source. Even after +resetting a VM, the old firmware is used. Only once QEMU has been restart= ed +is the new firmware in use. + +- Changes in firmware size can cause changes in the required RAMBlock size + to hold the firmware and thus migration can fail. In practice it's best + to pad firmware images to convenient powers of 2 with plenty of space + for growth. + +- Care should be taken with device emulation code so that newer + emulation code can work with older firmware to allow forward migration. + +- Care should be taken with newer firmware so that backward migration + to older systems with older device emulation code will work. + +In some cases it may be best to tie specific firmware versions to specific +versioned machine types to cut down on the combinations that will need +support. This is also useful when newer versions of firmware outgrow +the padding. diff --git a/docs/devel/migration/index.rst b/docs/devel/migration/index.rst index 7fc02b9520..c09623b38f 100644 --- a/docs/devel/migration/index.rst +++ b/docs/devel/migration/index.rst @@ -11,3 +11,4 @@ QEMU live migration works. compatibility vfio virtio + best-practises diff --git a/docs/devel/migration/main.rst b/docs/devel/migration/main.rst index b3e31bb52f..97811ce371 100644 --- a/docs/devel/migration/main.rst +++ b/docs/devel/migration/main.rst @@ -52,27 +52,6 @@ All these migration protocols use the same infrastructur= e to save/restore state devices. This infrastructure is shared with the savevm/loadvm functionality. =20 -Debugging -=3D=3D=3D=3D=3D=3D=3D=3D=3D - -The migration stream can be analyzed thanks to ``scripts/analyze-migration= .py``. - -Example usage: - -.. code-block:: shell - - $ qemu-system-x86_64 -display none -monitor stdio - (qemu) migrate "exec:cat > mig" - (qemu) q - $ ./scripts/analyze-migration.py -f mig - { - "ram (3)": { - "section sizes": { - "pc.ram": "0x0000000008000000", - ... - -See also ``analyze-migration.py -h`` help for more options. - Common infrastructure =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D =20 @@ -970,26 +949,3 @@ the background migration channel. Anyone who cares ab= out latencies of page faults during a postcopy migration should enable this feature. By default, it's not enabled. =20 -Firmware -=3D=3D=3D=3D=3D=3D=3D=3D - -Migration migrates the copies of RAM and ROM, and thus when running -on the destination it includes the firmware from the source. Even after -resetting a VM, the old firmware is used. Only once QEMU has been restart= ed -is the new firmware in use. - -- Changes in firmware size can cause changes in the required RAMBlock size - to hold the firmware and thus migration can fail. In practice it's best - to pad firmware images to convenient powers of 2 with plenty of space - for growth. - -- Care should be taken with device emulation code so that newer - emulation code can work with older firmware to allow forward migration. - -- Care should be taken with newer firmware so that backward migration - to older systems with older device emulation code will work. - -In some cases it may be best to tie specific firmware versions to specific -versioned machine types to cut down on the combinations that will need -support. This is also useful when newer versions of firmware outgrow -the padding. --=20 2.41.0