1bf8a989a5
Before the patch, seg_max parameter was immutable and hardcoded to 126 (128 - 2) without respect to queue size. This has two negative effects: 1. when queue size is < 128, we have Virtio 1.1 specfication violation: (2.6.5.3.1 Driver Requirements) seq_max must be <= queue_size. This violation affects the old Linux guests (ver < 4.14). These guests crash on these queue_size setups. 2. when queue_size > 128, as was pointed out by Denis Lunev <den@virtuozzo.com>, seg_max restrics guest's block request length which affects guests' performance making them issues more block request than needed. https://lists.gnu.org/archive/html/qemu-devel/2017-12/msg03721.html To mitigate this two effects, the patch adds the property adjusting seg_max to queue size automaticaly. Since seg_max is a guest visible parameter, the property is machine type managable and allows to choose between old (seg_max = 126 always) and new (seg_max = queue_size - 2) behaviors. Not to change the behavior of the older VMs, prevent setting the default seg_max_adjust value for older machine types. Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com> Signed-off-by: Denis Plotnikov <dplotnikov@virtuozzo.com> Message-Id: <20191220140905.1718-2-dplotnikov@virtuozzo.com> Reviewed-by: Michael S. Tsirkin <mst@redhat.com> Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
91 lines
2.0 KiB
C
91 lines
2.0 KiB
C
/*
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* Virtio Block Device
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*
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* Copyright IBM, Corp. 2007
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*
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* Authors:
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* Anthony Liguori <aliguori@us.ibm.com>
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*
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* This work is licensed under the terms of the GNU GPL, version 2. See
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* the COPYING file in the top-level directory.
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*
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*/
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#ifndef QEMU_VIRTIO_BLK_H
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#define QEMU_VIRTIO_BLK_H
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#include "standard-headers/linux/virtio_blk.h"
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#include "hw/virtio/virtio.h"
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#include "hw/block/block.h"
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#include "sysemu/iothread.h"
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#include "sysemu/block-backend.h"
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#define TYPE_VIRTIO_BLK "virtio-blk-device"
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#define VIRTIO_BLK(obj) \
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OBJECT_CHECK(VirtIOBlock, (obj), TYPE_VIRTIO_BLK)
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/* This is the last element of the write scatter-gather list */
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struct virtio_blk_inhdr
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{
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unsigned char status;
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};
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struct VirtIOBlkConf
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{
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BlockConf conf;
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IOThread *iothread;
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char *serial;
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uint32_t request_merging;
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uint16_t num_queues;
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uint16_t queue_size;
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bool seg_max_adjust;
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uint32_t max_discard_sectors;
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uint32_t max_write_zeroes_sectors;
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bool x_enable_wce_if_config_wce;
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};
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struct VirtIOBlockDataPlane;
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struct VirtIOBlockReq;
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typedef struct VirtIOBlock {
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VirtIODevice parent_obj;
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BlockBackend *blk;
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void *rq;
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QEMUBH *bh;
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VirtIOBlkConf conf;
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unsigned short sector_mask;
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bool original_wce;
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VMChangeStateEntry *change;
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bool dataplane_disabled;
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bool dataplane_started;
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struct VirtIOBlockDataPlane *dataplane;
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uint64_t host_features;
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size_t config_size;
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} VirtIOBlock;
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typedef struct VirtIOBlockReq {
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VirtQueueElement elem;
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int64_t sector_num;
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VirtIOBlock *dev;
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VirtQueue *vq;
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struct virtio_blk_inhdr *in;
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struct virtio_blk_outhdr out;
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QEMUIOVector qiov;
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size_t in_len;
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struct VirtIOBlockReq *next;
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struct VirtIOBlockReq *mr_next;
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BlockAcctCookie acct;
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} VirtIOBlockReq;
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#define VIRTIO_BLK_MAX_MERGE_REQS 32
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typedef struct MultiReqBuffer {
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VirtIOBlockReq *reqs[VIRTIO_BLK_MAX_MERGE_REQS];
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unsigned int num_reqs;
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bool is_write;
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} MultiReqBuffer;
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bool virtio_blk_handle_vq(VirtIOBlock *s, VirtQueue *vq);
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#endif
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