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charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable MIME-Version: 1.0 X-OriginatorOrg: epam.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-AuthSource: VI1PR03MB3710.eurprd03.prod.outlook.com X-MS-Exchange-CrossTenant-Network-Message-Id: 43913f52-dfba-429d-9eb3-08dbbbb7a374 X-MS-Exchange-CrossTenant-originalarrivaltime: 22 Sep 2023 22:02:39.8492 (UTC) X-MS-Exchange-CrossTenant-fromentityheader: Hosted X-MS-Exchange-CrossTenant-id: b41b72d0-4e9f-4c26-8a69-f949f367c91d X-MS-Exchange-CrossTenant-mailboxtype: HOSTED X-MS-Exchange-CrossTenant-userprincipalname: OypXTrO01kLa2hTNG0qVA7rtYHyPxpkvzpA/JzmxiZPP3DVo+sjMNL+WxwR9jgDMLXqlM9t0Pjmm49zweDJ0jp1BxSVQPctity4Z/0Cl68k= X-MS-Exchange-Transport-CrossTenantHeadersStamped: GV2PR03MB9450 X-Proofpoint-GUID: Zk2IJEgEzsmzKs66AmMJAu_MHhXbzCIE X-Proofpoint-ORIG-GUID: Zk2IJEgEzsmzKs66AmMJAu_MHhXbzCIE X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.267,Aquarius:18.0.980,Hydra:6.0.619,FMLib:17.11.176.26 definitions=2023-09-22_19,2023-09-21_01,2023-05-22_02 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 priorityscore=1501 impostorscore=0 clxscore=1015 malwarescore=0 phishscore=0 mlxlogscore=659 mlxscore=0 spamscore=0 adultscore=0 lowpriorityscore=0 bulkscore=0 suspectscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2309180000 definitions=main-2309220188 Hello Marc, Marc Zyngier writes: > Volodymyr, > > On Fri, 22 Sep 2023 01:22:11 +0100, > Volodymyr Babchuk wrote: >>=20 >>=20 >> Hi Mark, > > s/k/c/ Oh, I'm sorry. >>=20 >> I am writing to you, because you are GICv3 maintainer in Linux. We are >> updating ITS driver in Xen and we have a question about cache >> maintenance WRT memory shared with ITS. As I can see, the Linux ITS >> driver uses gic_flush_dcache_to_poc() all over the code. This boils down >> to "dc civac" instruction which does both clean and invalidate. But do >> we really need to invalidate a cache when we are sending an ITS command? >> In my understanding it is sufficient to clean a cache only and Linux >> uses clean&invalidate just out of convenience. Is this correct? > > It really depends how you look at it. We use DC CIVA as the standard > way to give a buffer to a device, as that's what the DMA API > does. Switching to a simple clean is possible, but I don't really see > what it brings you. > > ITS commands are usually written as a single command followed by a > SYNC/VSYNC. That's a total a 8 64bit words, which makes a cache line > on 99.999% of the implementations. > > What do you gain by keeping the cache line around? Not much. By the > time you go around the command queue and need the same data again, it > will have been evicted from your L1 already. This is a great point. Thank you. --=20 WBR, Volodymyr=