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([2601:ce:c180:9af0:e7b2:69d1:2d5a:7b37]) by smtp.gmail.com with ESMTPSA id 956f58d0204a3-65314b2845asm10434231d50.3.2026.04.24.01.28.29 for (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 24 Apr 2026 01:28:29 -0700 (PDT) Message-ID: Date: Fri, 24 Apr 2026 04:28:28 -0400 Precedence: bulk X-Mailing-List: linux-wireless@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Content-Language: en-US To: linux-wireless@vger.kernel.org From: Jayden Fowler Subject: mac80211 HT/VHT MCS check change causing Wi-Fi speed drop (~20 Mbps cap) on iwlwifi Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit Hello, I think I’ve run into a regression in mac80211 that affects Wi-Fi speeds on Intel iwlwifi (and possibly some Realtek cards too). After testing a bunch of kernels, I noticed something pretty consistent: Kernels with this commit Wi-Fi gets stuck around ~20 Mbps max Kernels without it (or after removing a small part of it) speeds go back to normal (hundreds of Mbps as expected) The commit I bisected it to is: 574faa0e936d12718e2cadad11ce1e184d9e5a32 "wifi: mac80211: add HT and VHT basic set verification" The issue seems to come from the new HT/VHT MCS verification logic. When it runs, it sometimes decides the AP’s advertised rates are “unsupported” and then forces a downgrade in connection mode/bandwidth. That downgrade looks like it’s what causes the big speed drop. When I remove this from `net/mac80211/mlme.c`, Wi-Fi goes back to normal speeds: if (conn->mode >= IEEE80211_CONN_MODE_HT &&     !ieee80211_verify_sta_ht_mcs_support(sdata, sband,                                          elems->ht_operation)) {     conn->mode = IEEE80211_CONN_MODE_LEGACY;     conn->bw_limit = IEEE80211_CONN_BW_LIMIT_20;     link_id_info(sdata, link_id,                  "required MCSes not supported, disabling HT\n"); } if (conn->mode >= IEEE80211_CONN_MODE_VHT &&     !ieee80211_verify_sta_vht_mcs_support(sdata, link_id, sband, elems->vht_operation)) {     conn->mode = IEEE80211_CONN_MODE_HT;     conn->bw_limit = min_t(enum ieee80211_conn_bw_limit,                            conn->bw_limit,                            IEEE80211_CONN_BW_LIMIT_40);     link_id_info(sdata, link_id,                  "required MCSes not supported, disabling VHT\n"); } This is my wifi card i'm testing on Network controller: Intel Corporation Dual Band Wireless-AC 3168NGW [Stone Peak] (rev 10) Thanks, Jayden Fowler.