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dkim=none (message not signed) header.d=none;intel.com; dmarc=none action=none header.from=amd.com; Received: from MN2PR12MB3775.namprd12.prod.outlook.com (2603:10b6:208:159::19) by MN2PR12MB4551.namprd12.prod.outlook.com (2603:10b6:208:263::22) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.4129.25; Wed, 19 May 2021 10:43:55 +0000 Received: from MN2PR12MB3775.namprd12.prod.outlook.com ([fe80::6d4d:4674:1cf6:8d34]) by MN2PR12MB3775.namprd12.prod.outlook.com ([fe80::6d4d:4674:1cf6:8d34%6]) with mapi id 15.20.4129.032; Wed, 19 May 2021 10:43:55 +0000 Subject: Re: [PATCH] drm/ttm: Explain why ttm_bo_add_move_fence uses a shared slot To: Daniel Vetter , DRI Development References: <20210519082409.672016-1-daniel.vetter@ffwll.ch> From: =?UTF-8?Q?Christian_K=c3=b6nig?= Message-ID: Date: Wed, 19 May 2021 12:43:49 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.8.1 In-Reply-To: <20210519082409.672016-1-daniel.vetter@ffwll.ch> Content-Type: text/plain; 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I think this is non-obvious enough that it merits a slightly > longer comment. > > Cc: Christian König > Cc: Christian Koenig > Cc: Huang Rui > Cc: Thomas Hellström > Signed-off-by: Daniel Vetter Reviewed-by: Christian König > --- > drivers/gpu/drm/ttm/ttm_bo.c | 4 +++- > 1 file changed, 3 insertions(+), 1 deletion(-) > > diff --git a/drivers/gpu/drm/ttm/ttm_bo.c b/drivers/gpu/drm/ttm/ttm_bo.c > index ca1b098b6a56..51a94fd63bd7 100644 > --- a/drivers/gpu/drm/ttm/ttm_bo.c > +++ b/drivers/gpu/drm/ttm/ttm_bo.c > @@ -682,7 +682,9 @@ int ttm_mem_evict_first(struct ttm_device *bdev, > } > > /* > - * Add the last move fence to the BO and reserve a new shared slot. > + * Add the last move fence to the BO and reserve a new shared slot. We only use > + * a shared slot to avoid unecessary sync and rely on the subsequent bo move to > + * either stall or use an exclusive fence respectively set bo->moving. > */ > static int ttm_bo_add_move_fence(struct ttm_buffer_object *bo, > struct ttm_resource_manager *man,