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Date: Thu, 26 Feb 2015 15:21:15 +0200 From: Eyal Birger <eyal.birger@...il.com> To: David Laight <David.Laight@...lab.com> Cc: "davem@...emloft.net" <davem@...emloft.net>, "willemb@...gle.com" <willemb@...gle.com>, "edumazet@...gle.com" <edumazet@...gle.com>, "shmulik.ladkani@...il.com" <shmulik.ladkani@...il.com>, "marcel@...tmann.org" <marcel@...tmann.org>, "netdev@...r.kernel.org" <netdev@...r.kernel.org> Subject: Re: [PATCH net-next 2/7] net: bluetooth: compact struct bt_skb_cb by converting boolean fields to bit fields Hi, On Thu, Feb 26, 2015 at 1:31 PM, David Laight <David.Laight@...lab.com> wrote: > From: Eyal Birger >> On 64 bit systems, struct bt_skb_cb size is padded by 6 bytes in order >> to reach 8 byte alignment. >> Convert boolean fields force_active, incoming and req_start to bit fields >> in order to eliminate the padding. > ... >> +++ b/include/net/bluetooth/bluetooth.h > ... >> struct bt_skb_cb { >> __u8 pkt_type; >> - __u8 incoming; >> __u16 opcode; >> __u16 expect; >> - __u8 force_active; >> - bool req_start; >> + __u8 force_active:1; >> + __u8 incoming:1; >> + __u8 req_start:1; >> u8 req_event; >> hci_req_complete_t req_complete; >> struct l2cap_chan *chan; > > You've generated some pad bytes, best to put everything on its natural alignment. > The old version had req_complete at offset 9, the new one at offset 8. > Not sure how this removes 6 bytes of pad. > Hmm, I tried different variations here. At a certain point, I had 6 bytes of padding. Seems pahole is playing peekaboo on my holes :) Anyway, since req_complete has to be pointer aligned, it does not reside at offset 9, but at offset 16, which creates a hole. Thanks. I will update appropriately in v2. -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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